As you said, map creators should make the map beautiful, but they also need to make sure that when building decorations, players cannot abuse them (for example, walking through textures)
If you are allowed to change the skin of your pets, it will certainly be very cool, but some players may abuse this. For example, if a player paints lvl 380 fairy-pets the same color as lvl 1650 fairy-pets, this can bring disaster. Some player, running away from mobs, can lead them to painted fairies, which can cause them to die. In this case, this unfortunate player maybe sent to prison.
But if you can paint your pets without such consequences, then I will be all for it!