In the process of painting you focus your attention on a subject that is at your fingertips. If you do it with enough concentration, it will ignore the extraneous noise, unpleasant thoughts and worries. This is a very useful skill that will be useful in situations where you need to briefly forget about your physical or emotional pain.
Coloring, of course, cannot be banned. You should not exclude its use for fine motor skills; this activity allows parents to get an extra half an hour of free time.