Sorry marcus but limewater is clear and colourless. When you bubble carbon dioxide through it it turns milky due to the formation of calcium carbonate (chalk). You are right about not drinking it - it is a strong alkali.
I wonder if there is something you can add to ordinary milk to stop it turning sour? Adding something acidic, such as lemon juice, might work. I'm not sure though.
how about paint block like the type schools use for brush art, I imagine it's safe, you know, the kind you dip the brush in water then rub the block with it to paint pictures.