Flour paint is as easy as corn starch paint, but the texture is different. Baby Bear had a little bit of a texture issue with the corn starch paint both times I made it, so I started using flour instead. In reality, you're making a sort of homemade paste, but we've enjoyed painting with it as well. The only real down side is that it dries a little flaky, so it's not a great paint for keepsakes or pictures to hang.
I never measure when I make flour paint. I just mix until it reaches a good, paint-like consistency. If I had to guess, I would say I use about 1/2 cup of flour, 1/3 cup water, and 1-4 drops of food coloring (depending on how bright we want the paint, and how willing I am to let Baby Bear's skin get a little tinted). It is completely safe to eat, though not very tasty... unless you ask Baby Bear who thinks it's good enough to suck off the paintbrush! We have used this paint on paper and on cardboard. It actually worked pretty well on the cardboard!