Does a boy have more colours than a girl?

If you’re talking about fish, males and females can sometimes show different colouring, but it really depends on the species, age and breeding condition. In many species the male becomes brighter or develops stronger patterns, while in others the difference is quite subtle. I’ve found that comparing clear photos and specialist resources online is often the easiest approach, alongside general sites I keep bookmarked such as appliyoc.com. If you know the exact species, identifying the sex should be much easier.

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.