# Why and How RGB? **URL:** \ **Category:** Factual Questions\ **Created:** [September 17, 2005, 12:45am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068 "2005-09-17T00:45:45Z")\ **Posts on this page:** 14\ **Page:** 1
**Author:** ![Zebra](https://avatars.discourse-cdn.com/v4/letter/z/c0e974/32.png) [@Zebra](https://boards.straightdope.com/u/Zebra)\ **Post date:** [September 17, 2005, 12:45am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/1 "2005-09-17T00:45:45Z")
and not RBY? Red, Blu and Yellow are the primary colors. But Red Green Blue are settings on my monitor. Why isn’t my monitor/TV etc RGY? And How does RGB combine to make yellows? ---
**Author:** ![ouryL](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/ouryl/32/6067_2.png) [@ouryL](https://boards.straightdope.com/u/ouryL)\ **Post date:** [September 17, 2005, 12:57am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/2 "2005-09-17T00:57:03Z")
Go play with your moniter controls. If you have a PC and are using Windows, you can control the color of your background by changes the RGB values. [COLORS](http://www.webdiner.com/annexe/hexcode/hexcode.htm) ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [September 17, 2005, 1:01am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/3 "2005-09-17T01:01:47Z")
Pigment primary colours are actually cyan, yellow and magenta (red, blue and yellow are primary school art class approximations); light primary colours are red, green and blue. This is because pigments work by absorbing light and only reflecting back a part of it, so every time you add a pigment of another colour, you’re reducing the total range of colours of light being reflected - pigment primaries are _subtractive_. Light primaries are _additive_ - every different colour of light you shine on a surface (or _out of it_, in the case of light emitting devices), _ **adds** _ to the total range of colours of light being perceived. ---
**Author:** ![panamajack](https://avatars.discourse-cdn.com/v4/letter/p/47e85d/32.png) [@panamajack](https://boards.straightdope.com/u/panamajack)\ **Post date:** [September 17, 2005, 1:08am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/4 "2005-09-17T01:08:40Z")
Magenta(reddish), cyan(bluish), and yellow are the primary colors used for _subtractive_ color mixing. Red, green, and blue are the primary colors used for _additive_ color mixing. The monitor produces red, green, and blue colored light. Shining a red, blue, and green light together produces white light (you’ve added up enough light to cover the visible spectrum). Red, green, and blue are also what the three types of cones in the eye respond to. Subtractive color works by filtering out light leaving only a particular color. If you combine the primary color filters magenta, cyan, and yellow you get black (you’ve filtered out enough light to block the visible spectrum). [The Hyperphysics site](http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html) explains color in a lot more detail, with diagrams. ---
**Author:** ![panamajack](https://avatars.discourse-cdn.com/v4/letter/p/47e85d/32.png) [@panamajack](https://boards.straightdope.com/u/panamajack)\ **Post date:** [September 17, 2005, 1:09am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/5 "2005-09-17T01:09:49Z")
Or, what **Mangetout** said. ---
**Author:** ![FlyingRamenMonster](https://avatars.discourse-cdn.com/v4/letter/f/ce7236/32.png) [@FlyingRamenMonster](https://boards.straightdope.com/u/FlyingRamenMonster)\ **Post date:** [September 17, 2005, 1:16am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/6 "2005-09-17T01:16:43Z")
Red and green makes yellow. If you draw on the computer you get very used to it after a while. ---
**Author:** ![dre2xl](https://avatars.discourse-cdn.com/v4/letter/d/34f0e0/32.png) [@dre2xl](https://boards.straightdope.com/u/dre2xl)\ **Post date:** [September 17, 2005, 1:49am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/7 "2005-09-17T01:49:34Z")
There are 3 types of color-detecting cones in your eyes; each type responds to a different range of wavelengths in the light spectrum. Very roughly, these types “peak” at red, green, and blue, correspondingly. If an intermediate wavelength comes in (say, yellow), then more than one type of cone will get excited. In the case of yellow, for example, both red & green cone types will become excited, and the brain sees the color yellow. So, every color can be conceived with a mixture of red, green, and blue wavelengths, because in a way that’s all we can see. I’ve always wondered what a hypothetical person with more than 3 types of cones would perceive if they saw a TV. Probably would look monotone or washed-out to them. ---
**Author:** ![Netbrian](https://avatars.discourse-cdn.com/v4/letter/n/71e660/32.png) [@Netbrian](https://boards.straightdope.com/u/Netbrian)\ **Post date:** [September 17, 2005, 2:23am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/8 "2005-09-17T02:23:15Z")
> [@dre2xl](#): > > I’ve always wondered what a hypothetical person with more than 3 types of cones would perceive if they saw a TV. Probably would look monotone or washed-out to them. There’s some research indicating such people actually exist – Google tetrachromats. ---
**Author:** ![friedo](https://avatars.discourse-cdn.com/v4/letter/f/8edcca/32.png) [@friedo](https://boards.straightdope.com/u/friedo)\ **Post date:** [September 17, 2005, 2:42am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/9 "2005-09-17T02:42:42Z")
> [@Netbrian](#): > > There’s some research indicating such people actually exist – Google tetrachromats. I could have sworn I read an article once about some women who were tetrachromats, but Wikipedia [says](http://en.wikipedia.org/wiki/Tetrachromacy) it’s never been confirmed in mammals. ---
**Author:** ![dre2xl](https://avatars.discourse-cdn.com/v4/letter/d/34f0e0/32.png) [@dre2xl](https://boards.straightdope.com/u/dre2xl)\ **Post date:** [September 17, 2005, 2:50am UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/10 "2005-09-17T02:50:09Z")
If human tetrachromats really existed in modern times, there’d be a LOT more literature on them. Color science is a very big field spanning many industries. ---
**Author:** ![Zebra](https://avatars.discourse-cdn.com/v4/letter/z/c0e974/32.png) [@Zebra](https://boards.straightdope.com/u/Zebra)\ **Post date:** [September 17, 2005, 2:22pm UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/11 "2005-09-17T14:22:37Z")
Thanks, So, if I’m working with paint, I can mix red, blue and yellow together to make the colors, but if I’m projecting an image I would use RBG. Is that about it? ---
**Author:** ![Arjuna34](https://avatars.discourse-cdn.com/v4/letter/a/eb8c5e/32.png) [@Arjuna34](https://boards.straightdope.com/u/Arjuna34)\ **Post date:** [September 17, 2005, 3:20pm UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/12 "2005-09-17T15:20:47Z")
Cecil himself has addressed this: [If blue, red, and yellow are primary colors, why do color TVs use blue, red, and green?](http://www.straightdope.com/classics/a3_344.html) Arjuna34 ---
**Author:** ![Fish](https://avatars.discourse-cdn.com/v4/letter/f/bc8723/32.png) [@Fish](https://boards.straightdope.com/u/Fish)\ **Post date:** [September 17, 2005, 3:53pm UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/13 "2005-09-17T15:53:29Z")
> [@Zebra](#): > > So, if I’m working with paint, I can mix red, blue and yellow together to make the colors, but if I’m projecting an image I would use RBG. Is that about it? More or less, yes. As noted above, you’d need cyan, magenta and yellow paints (plus black to make dark colors). We only call them “red,” “blue” and “yellow” to schoolchildren who haven’t learned as many proper color names. You might also note that Cyan, Magenta, Yellow and blacK combine into what is called CMYK four-color printing. Check out the margins of your newspaper sometime on any page where color is printed; you might find little crosshairs in cyan, magenta, yellow and black. These crosshairs are supposed to line up so that each color in the printing process aligns properly with the others, but often newspapers are imprecise enough to see each crosshair color separately. I’ve actually drawn color renderings using only cyan, magenta and yellow Prismacolor pencils (with black for shadows). You can get quite a range of color if you practice your color blending. ---
**Author:** ![Napier](https://avatars.discourse-cdn.com/v4/letter/n/ce73a5/32.png) [@Napier](https://boards.straightdope.com/u/Napier)\ **Post date:** [September 18, 2005, 7:38pm UTC](https://boards.straightdope.com/t/why-and-how-rgb/322068/14 "2005-09-18T19:38:06Z")
\>So, every color can be conceived with a mixture of red, green, and blue wavelengths, because in a way that’s all we can see. This isn’t actually true, because our three kinds of cones each have broad ranges of sensitivities, and the ranges overlap. Moreover, our red cones also have a small sensitivity peak in the blue. Mixing any triad of real colors can only create colors inside a triangle in “color space”, having its angle points at the real colors locations. The human color range is a somewhat rounded and bulging triangle in this space; no real triangle covers all the points inside our bulging triangle. Color experts, such as the “CIE”, create imaginary colors called X, Y and Z such that X + white = pure red, y + white = pure green, and Z + white = pure blue. These colors can’t physically exist, but some linear combinations of them can, and they fill out the human “gamut” or range of colors. Mathematically this works out just fine and solves many problems in color science.