Laura might be half-hispanic depending on what source material one draws from, but obviously was made in a lab and doesn't know where she comes from outside of Logan, and it affects her whole character.
Race isn't a big part of Rogue, but her southeast-US heritage is - the way she talks, the food she eats, etc. Also she has yet to elaborate on her backstory much almost certainly because she's hiding the secret that she was adopted by Mystique and that's the "difficult family" she's been getting those phone calls from in the game.
When we get to Storm next season, that's a character who used to be worshipped as a goddess by an African tribe. There's no way that doesn't affect how a person sees themselves.
Psylocke could be written to have feelings about being of mixed heritage, of being different from her brothers, or of being the product of a relationship similar to Null's if the writers decide to go in any of those directions. Those would all be big factors in a person's upbringing that would shape their life and personality and honestly it'd be a waste for a writer to disregard the opportunity to flesh her out.
