¼ cup self-raising flour
¼ cup salt
½ cup water
Food colour (1-2 TBSP)
Large cup / mixing bowl
Make Time: Less than 7 minutes.
Keep a stash of already mixed solid ingredients (ratio 1:1) and separate coloured water bottles. Whenever you need paint, just whisk out a cup and mix the two in a ratio of 1:1.
The liquid paint should stay fresh for 2-3 weeks depending on the heat / humidity in your area. You may also refrigerate.
Related: Simple Pendulum Painting