The anime one is an interesting example, because I've seen the perspective in the anime community is that trans people are also disproportionately common there, similar to your mention that anime is an interest that is disproportionately common among trans communities.

The common brightly coloured hair seems to come from the fact that society is not fully accepting of trans people and depending on the level of that in your social circles, it may feel like you need to break a taboo just to be yourself, so other social expectations (like modest hair colours) are also downgraded in importance.