It is cake icing coloring, in walmart's craft department, with the wedding decorations stuff.
Here's a sample of the red and purple. It is so thick and dark that I had to water it down.
And, considering it's use, it must be safe to eat.

Just dip a small brush in some water to get it good and wet, and just touch a tip of the brush into the coloring.
Much easier than the messy koolaid or food colorings.
I went back this morning and bought yellow, blue, green and orange.
Oh, yeah, and it only cost $1.27 per jar.