I've just reminded myself...
When I was younger, I used to get a few tubs of play-doh, usually a blue, possibly a red if I was feeling risqué, hide behind the curtains in the hallway and stuff as much into my gob as possible before I was rumbled.

Something in the combination of digesting brightly coloured modelling clay and the stress of my guerilla eating habits played havoc with my bowels, however.

The look of supreme disappointment on my mother's face as she drew back the twitching curtains to reveal my ridiculous, grinning, blue face still haunts me.

Made for some very interesting poos, though.
( SigmaX0 Dear Die Hard. You rock!, Wed 1 Jun 2011, 14:42, 2 replies)

Snails do this too
Do poos that directly reflect the colour of their last meal, I mean.
In fact, I had a QOTW front page post on this very subject a couple of years back.
(Juan Quar is clinging to her front teeth on, Wed 1 Jun 2011, 16:02, closed)

would be more impressive
if the poo came out in crescent/star/square shape
(Monkeystrumpet monkey. Monkey, MONKEY!!!, Thu 2 Jun 2011, 15:28, closed)