# How many colors? (cool optical illusion) **URL:** \ **Category:** Miscellaneous and Personal Stuff I Must Share\ **Created:** [June 25, 2009, 5:17am UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912 "2009-06-25T05:17:48Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![otorophile](https://avatars.discourse-cdn.com/v4/letter/o/3ab097/32.png) [@otorophile](https://boards.straightdope.com/u/otorophile)\ **Post date:** [June 25, 2009, 5:17am UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/1 "2009-06-25T05:17:48Z")
[http://blogs.discovermagazine.com/badastronomy/2009/06/24/the-blue-and-the-green/](http://blogs.discovermagazine.com/badastronomy/2009/06/24/the-blue-and-the-green/) This is one of the more compelling optical illusions I’ve seen. It really looks like there are 3 different colors in there. Actually, while I’m at it, here’s another cool trick of the mind: [http://www.johnsadowski.com/big\_spanish\_castle.php](http://www.johnsadowski.com/big_spanish_castle.php) ---
**Author:** ![Cisco](https://avatars.discourse-cdn.com/v4/letter/c/ccd318/32.png) [@Cisco](https://boards.straightdope.com/u/Cisco)\ **Post date:** [June 25, 2009, 5:40am UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/2 "2009-06-25T05:40:11Z")
The guy who writes the Bad Astronomy blog - Phil Plait - used to post here. ---
**Author:** ![Rigamarole](https://avatars.discourse-cdn.com/v4/letter/r/77aa72/32.png) [@Rigamarole](https://boards.straightdope.com/u/Rigamarole)\ **Post date:** [June 25, 2009, 6:07am UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/3 "2009-06-25T06:07:09Z")
> [@otorophile](#): > > This is one of the more compelling optical illusions I’ve seen. It really looks like there are 3 different colors in there. You mean it looks like there are 4 different colors, right? There are 3: magenta, orange (the stripes), and the bluish green used for the spirals. Anyway, very cool. ---
**Author:** ![Gatopescado](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gatopescado/32/5711_2.png) [@Gatopescado](https://boards.straightdope.com/u/Gatopescado)\ **Post date:** [June 25, 2009, 6:11am UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/4 "2009-06-25T06:11:54Z")
I’m really starting to think that the folks who are paying (like I used to) and not seeing these ads are missing out on half the fun of these threads. WTF is the above ad for? Every bit as entertaining as the two links in the OP however. 😃 ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [June 25, 2009, 6:27am UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/5 "2009-06-25T06:27:24Z")
There’s a black and white [variation](http://www.dailycognition.com/index.php/2009/02/19/20-incredible-optical-illusions.html) of this illusion. (Scroll down to #18) ---
**Author:** ![BigT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bigt/32/12044_2.png) [@BigT](https://boards.straightdope.com/u/BigT)\ **Post date:** [June 25, 2009, 6:49am UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/6 "2009-06-25T06:49:48Z")
> [@Rigamarole](#): > > You mean it looks like there are 4 different colors, right? > > There are 3: magenta, orange (the stripes), and the bluish green used for the spirals. > > Anyway, very cool. Yeah. That confused me so much that I didn’t figure out what the illusion was supposed to be like I usually do. I should have guessed that the “blue” and “green”, since they appeared as variations of the same color, were actually the same color. Incidentally, I wish the Gimp (or even Photoshop) had a perceptive colors option, so that the color would automatically change depending on what colors were around it. Instead, I’ll have to play around to figure out what color those appear to be. > [@Little\_Nemo](#): > > There’s a black and white [variation](http://www.dailycognition.com/index.php/2009/02/19/20-incredible-optical-illusions.html) of this illusion. (Scroll down to #18) That’s the one I’m familiar with. That’s why I’m surprised I didn’t recognize this one. ---
**Author:** ![otorophile](https://avatars.discourse-cdn.com/v4/letter/o/3ab097/32.png) [@otorophile](https://boards.straightdope.com/u/otorophile)\ **Post date:** [June 25, 2009, 12:56pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/7 "2009-06-25T12:56:37Z")
> [@Rigamarole](#): > > You mean it looks like there are 4 different colors, right? I meant three different colored spirals. My wording was unclear. ---
**Author:** ![Munch](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/munch/32/5281_2.png) [@Munch](https://boards.straightdope.com/u/Munch)\ **Post date:** [June 25, 2009, 1:54pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/8 "2009-06-25T13:54:39Z")
> [@Gatopescado](#): > > WTF is the above ad for? Every bit as entertaining as the two links in the OP however. 😃 I believe the ads are different for everyone. ---
**Author:** ![Malleus\_Incus\_Stapes](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/malleus_incus_stapes/32/3293_2.png) [@Malleus\_Incus\_Stapes](https://boards.straightdope.com/u/Malleus_Incus_Stapes)\ **Post date:** [June 25, 2009, 2:16pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/9 "2009-06-25T14:16:59Z")
> [@otorophile](#): > > Actually, while I’m at it, here’s another cool trick of the mind: > > [http://www.johnsadowski.com/big\_spanish\_castle.php](http://www.johnsadowski.com/big_spanish_castle.php) What… the…? I don’t have words. ---
**Author:** ![FoieGrasIsEvil](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/foiegrasisevil/32/16638_2.png) [@FoieGrasIsEvil](https://boards.straightdope.com/u/FoieGrasIsEvil)\ **Post date:** [June 25, 2009, 2:22pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/10 "2009-06-25T14:22:37Z")
> [@Malleus\_Incus\_Stapes](#): > > What… the…? > > I don’t have words. That one is cooler than the first one! ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 25, 2009, 3:23pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/11 "2009-06-25T15:23:44Z")
That’s very cool. I **really** like this one: [http://web.mit.edu/persci/people/adelson/checkershadow\_illusion.html](http://web.mit.edu/persci/people/adelson/checkershadow_illusion.html) ---
**Author:** ![Free\_Range\_Otter](https://avatars.discourse-cdn.com/v4/letter/f/ba8739/32.png) [@Free\_Range\_Otter](https://boards.straightdope.com/u/Free_Range_Otter)\ **Post date:** [June 25, 2009, 4:00pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/12 "2009-06-25T16:00:07Z")
Can someone explain (using small words) how that castle illusion works? It’s truly amazing. ---
**Author:** ![beowulff](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/beowulff/32/542_2.png) [@beowulff](https://boards.straightdope.com/u/beowulff)\ **Post date:** [June 25, 2009, 4:15pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/13 "2009-06-25T16:15:21Z")
> [@Free\_Range\_Otter](#): > > Can someone explain (using small words) how that castle illusion works? It’s truly amazing. The first image is a blurred negative of the color image. When you stare at it, you fatigue the color receptors in your eye. When you move the mouse onto the image, it is replaced by a B&W version of it. You then get an afterimage (which is the negative of the first color image) superimposed on top of it. Since the negative of the first image is the correct colors, it looks like a full color version. ---
**Author:** ![Bosstone](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@Bosstone](https://boards.straightdope.com/u/Bosstone)\ **Post date:** [June 25, 2009, 4:24pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/14 "2009-06-25T16:24:06Z")
The color illusions drive me nuts. Most illusions I can see through or manipulate once I understand the illusion; I can force myself to see ‘curved’ lines as straight, or flip the cube facing at will, for example. But I _cannot_ make myself see the ‘green’ and ‘blue’, or the ‘light grey’ and ‘dark grey’, as the same colors. When I sample the colors individually, I can see that they’re the same, but in context it’s impossible to bull through the illusion. That makes them special IMO. ---
**Author:** ![flyboy](https://avatars.discourse-cdn.com/v4/letter/f/4da419/32.png) [@flyboy](https://boards.straightdope.com/u/flyboy)\ **Post date:** [June 25, 2009, 5:03pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/15 "2009-06-25T17:03:35Z")
> [@FoieGrasIsEvil](#): > > That one is cooler than the first one! Holy crap. At first I had no clue what anyone was talking about–nothing changed for me when I moved the mouse over. Then I switched from Mozilla to IE, and… holy crap. ---
**Author:** ![Snickers](https://avatars.discourse-cdn.com/v4/letter/s/5daacb/32.png) [@Snickers](https://boards.straightdope.com/u/Snickers)\ **Post date:** [June 25, 2009, 5:57pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/16 "2009-06-25T17:57:21Z")
I know, hey? I was all, “nice joke - it \*is \*in color. They just put the color picture in the mouseover to fool with people.” Then totally did a double-take when my eyes moved and I saw it was in b&w all along. ---
**Author:** ![cochrane](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cochrane/32/10441_2.png) [@cochrane](https://boards.straightdope.com/u/cochrane)\ **Post date:** [June 25, 2009, 9:13pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/17 "2009-06-25T21:13:50Z")
> [@flyboy](#): > > Holy crap. At first I had no clue what anyone was talking about–nothing changed for me when I moved the mouse over. Then I switched from Mozilla to IE, and… holy crap. I doubt the browser makes a difference. I saw the color illusion just fine in Firefox. Of course, YMMV. ---
**Author:** ![Bosstone](https://avatars.discourse-cdn.com/v4/letter/b/22d042/32.png) [@Bosstone](https://boards.straightdope.com/u/Bosstone)\ **Post date:** [June 25, 2009, 9:20pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/18 "2009-06-25T21:20:31Z")
> [@flyboy](#): > > Holy crap. At first I had no clue what anyone was talking about–nothing changed for me when I moved the mouse over. Then I switched from Mozilla to IE, and… holy crap. Running NoScript? When a page doesn’t seem to work right, that’s always the first thing I check. I allowed the domain and it worked fine. ---
**Author:** ![NinetyWt](https://avatars.discourse-cdn.com/v4/letter/n/cc9497/32.png) [@NinetyWt](https://boards.straightdope.com/u/NinetyWt)\ **Post date:** [June 25, 2009, 9:46pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/19 "2009-06-25T21:46:25Z")
> [@Bosstone](#): > > But I _cannot_ make myself see the ‘green’ and ‘blue’, or the ‘light grey’ and ‘dark grey’, as the same colors. On this particular one, if you look at the very edge of the picture the colors seem much more similar. ---
**Author:** ![Inigo\_Montoya](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/inigo_montoya/32/124_2.png) [@Inigo\_Montoya](https://boards.straightdope.com/u/Inigo_Montoya)\ **Post date:** [June 25, 2009, 10:07pm UTC](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912/20 "2009-06-25T22:07:29Z")
> [@Munch](#): > > I believe the ads are different for everyone. No the ads are the same, they just _look_ different. [Next page](https://boards.straightdope.com/t/how-many-colors-cool-optical-illusion/500912.md?page=2)