Does a boy have more colours than a girl?

Yes, it almost all types of fish

In most fish species, the male gender is more colorful, vivid, and ornate than the female gender, but this isn’t the case with platyfish. The male platies tend to have more color and brightness than female platies, even though they often have the same patterns. 

You can also differentiate the male and female platies through the vibrant colors in their body. Like any other fish species, the male platies come with more vibrant colors and more complex patterns than the female because they naturally use them to attract their female counterparts to mate. But more or less, both the male and female platies come with similar patterns. You can identify them by the quality of the colors of the bird. It is also normal for the male platies to have darker hues than their female counterpart.