I recently had an essay on kids and advertisements. We stumbled on colors as well, given that it is an advertising trick to attract kids. On a research, conducted by a Psychology professor in the University of California, it showed that certain colors affect psychology.
For example, green has to do with calmness and relaxation, black has to do with generally bad mood, red has to do with aggression, etc.
The same research showed the results of a test: When children were given certain pictures that depicted happy scenes, they were then told to shape something in the color of their choice; when they were given happy scenes, the children were always choosing intense colors, such as blue, yellow or green. When they were shown sad scenes, they were coloring in brown, dark blue or grey.
Colors are just colors, they are reflections and products of light. They have a psychological impact on us, because we learned to identify colors and link them with certain meanings or situations. Yellow being bad luck for example is nothing but a superstition. Red being the color of passion is again a bond, created by social influence. Pink being particularly a girls' color is again socially structured. The world wasn't created with pink being a girls' color nor blue being the boys' one. It's how people interpret them, creating a vicious circle of knowledge, inherited to the societies. It's part of the social interaction and communication. Pink for example is no longer a taboo, to be worn as a t-shirt by boys, because certain fashion icons or fashion designers have included pink in their males' wear collections.
The further we go, the less taboo we will have, even in such a small matter, of what color to pick.