Melts in Your Mouth, Not in Your...Toilet???

As I got up this morning, and I went to the bathroom, I discovered that someone had been there before me. We usually have the rule "if it's yellow let it mellow, if it's brown flush it down."; but some of the younger members of our family don't quite get that yet. So needless to say I discovered Number Two fermenting in the bowl. But this particular specimen had tinted the water BLUE! What?!?!?!?!?! I thought back to the boys' meals yesterday and I could not find anything that would cause the poo to be blue. Then I remembered the M&M's bag I had found in the pantry, half-consumed... enough said.