I was in art therapy for 1.5 years. It didn't have much to do with colouring and exercises. It was Jungian based and we worked with archetypes, dreams, the unconscious, language. I get a bit agitated by people understanding art therapy as "ooo colouring is relaxing" or "complete these exercises to feel better". Art therapy is much more nuanced and the work is deep. I guess CBT is another ball game so maybe that approach fits with colour in a mandala and reset your negative thoughts.