Food and drink colorants.

[Winklabom]

wow! there is one in the game already?

Yep, here is the recipe straight from the Wiki:

Colorful Reagent= Plasma + Radium + Space Drugs + Cryoxadone + Triple Citrus (+ Stabilizing Agent)

It's harmless and colors anything it touches with a random color. Just use it a couple of times until you get the color you want.

I honestly believe that there should be a bottle of colorful reagent placed in the kitchen just like there is a bottle of hairgrownium in the barber's shop.