I found a few recipes online and they all seem about the same. For the dye you can use natural powders (such as beet and tumeric) or you can use a vegan food dye. Great blog here on making your own natural dyes!
1 cup plain flour
1 cup kosher salt
Add salt to about 1 cup hot water and stir till melted. I didn't do this and the paint was granulated.
Once salt has melted add the salt water to the flour and whisk til there are no lumps.
To get your desired consistency add more water.
Divide flour mix into different bowls (one for each colour).
Add dyes to each bowl and stir, adding more dye if needed, until the desired colour is reached.
Store in air tight containers.
NB: some people also add 1 tbls oil for shine but I didn't do this.