I would imagine I’m not the only Doper out there this happens to, so I am coming straight to the source for all the information.
Why in the world does purple grape juice, grape carbonated drinks and grape Kool-Aid turn one’s (ahem…!) feces BRIGHT GREEN? I know it must have something to do with the dyes in the drinks. But why green? And why doesn’t other artificially colored drinks turn it some other color? 
So that’s what happened to all the communion juice at church!
It ain’t easy being green!
By green do you mean green like the L in [color=“blue”]Google? Of course I’m referring to the L on their esteemed site not the one I just coded on here. Could you please give a hexadecimal equivalent because by your emphasis of green it puts me in the mind of the electric green which was so popular in the early eighties.
Here’s a link to help you.
http://hotwired.lycos.com/webmonkey/reference/color_codes/[/color]
They say a picture is worth a thousand words …
Perhaps on consumption junction but not on the straight dope. I think plenty of us are familair with how Mr. Hankey turns greenish when we imbibe too much grape soda or other purple foodstuffs. The mods can rest easy knowing I won’t be using my digital cameras to illustrate this thread.
Thanks, Steve, for starting off the responses with a joke! I thought you said you never do that! Now everyone thinks it’s a joke! Well, it IS funny, but I really do want to know WHY!
By the way, everybody, Padeye had his chance this morning to make light of this in private… he’s my fiancee and I told him I was posting this to the SDMB to find out. But NO… he waits until I submit the OP to make fun of my question. “Lucy, you have some ‘splainin’ to do when you get home tonight!”
Well, Raisin Bread, it’s like #669900, in all honesty! I mean, we’re talking GREEN!
Pure grape juice shouldn’t do that-check your label …
FD&C blue dye #1 in combination with the typical yellowish brown color of feces makes a bright green color. Other dyes evidently get metabolized in some way, but that one comes straight through.
I suppose the pre-emptive hijack was a bit out of line. I’ll take my lumps when I get home. Howsabout I bake a nice lasagne for dinner?
As for the question I can only make a guess and say what I did this morning that some substancs don’t break down in teh digestive process. The green color is probably just how it combines with other things like bilirubin.
For the record she didn’t ask me to see the color for myself and I thank her for that.
The only time my feces are yellowish brown is when I’m sick. Normally they are plain brown.
Is this getting to be too much of a TMI thread???
Accepted. 
Am I going to have to pull this car over?!?!?! Let’s get back to the OP!
I suspect that the mostly blue nature of Grape Juice dye, and the mostly yellowish-brown color of poo combine to make a green. I’ve seen anything from bright green to army drab, depending on the yellow stuff[sub]TM[/sub] content of the poopies.
I have noticed this too, when I drink large amounts of grape koolaid. Scared the crap out me the first time. Well, it WOULD have scared the crap out of me, if I hadn’t… Oh nevermind.
I notice a similar effect when I eat large amounts of Fruity Pebbles. Obviously some dye-related phenomenon.
I took a few pictures last time it happened, if you are curious.
Well, it’s better than what purple grape juice did to my brother when he was a little kid. Purple puke!
For those of you with JuiceMan juicing machines, if you really want a shock, buy some beets and make yourself a nice big glass of beet juice. Whatever it is that makes beets red is apparently indigestible, and your poo & your pee will both be bright fuschia colored!
I get colour #669900 too, when I’ve had too much red wine. Including homemade wines, actually, so I know that for me it ain’t the dyes.
Something occasionally makes my poo #999900 or #666600, and I don’t know what. I don’t drink grape kool-aid or red wine so I don’t know what it could be!
The first time I noticed the Beets Phenomenon that Fear Itself points out, I went straight to my internist, who was just about to send me for an expensive battery of tests, when he asked me if I’d eaten anything unusual lately.
Diagnosis: Borsht.
That should be: exTENsive. I mean, they were probably expensive too, but also complicated and lengthy.