There Are No Blue Mice(1959)

A family of mice meet a little blue mouse on their Sunday walk. The little mouse politely asks them to give him some of their cake. The mouse parents don't want to know anything about the strange fellow and forbid their children to have any contact with him. The little ones continue to play anyway. In a painter's studio, they discover various paint pots, and the horrified parents are suddenly presented with three colorful mice that they no longer know are their own children. When they are all washed up, three gray mice stand before them. In shock, the parents fall into a pot of blue paint and see that there can be blue mice after all.