Any lack of artistic representation can be resolved in this manner. Not enough black people, women, queers, poor people, seniors ...? Make. Display. Fix.
That means every unbalanced display that doesn't have a thematic reason for it (e.g. Famous Women will have only one gender) is unbalanced by choice. The moment anyone points out "Hey, there are 62 paintings here and all are white," it's time to fix that or admit to the bigotry.