ANSWER:

This is definitely sinful as this is racist!

Prophet salla Allahu alaihi wa sallam said that there is no superiority of a white person over a black and vice versa except through piety.

It’s very common in desi community to reject a girl or boy based on their color and mock them. Also parents and relatives criticize a child’s dark skin tone and comparing it to a buffalo’s or a crow’s. Is this sinful and is there any punishment for this?