My realty tax dollars at work, part deux

Younger's teacher said to me on one of younger's progress reports that younger does not colour things in their proper colours- i.e. she likes to colour horses purple.

Now, Bear's mother is an artist, so I mentioned this to her. "Proper colours!" she scoffed. "Phooey! Children should have fun with art." I should add my mother in law is a realist artist, who specializes in portraits, and loathes modern art. Apparently she suspends her dislikes for her grand children.

So I have a teacher on one hand and a trained artist on the other. To whom should I listen?