There are three types of authors when it comes to character description and, just like Goldilocks and her porridge, only one of them gets it just right. Of course, this means the other two provide way too much information or not nearly enough. It’s a fine line. It’s also difficult to please all readers in this area because some prefer a lot of description in order to have a comprehensive image of the character in their mind and some prefer the bare minimum so that they can do some of the imagining for themselves.
So does it matter what they look like? I’m going to use a few Shakespearean examples to answer the question. (Shakespeare’s plays are usually a great example of everything to do with writing.) Sometimes it doesn’t. In Kenneth Branagh’s film adaptation of Much Ado About Nothing, Denzel Washington and Keanu Reeves play the brothers Don Pedro and Don John. While Don John is described as a “bastard”, an illegitimate son, there is no mention of any specific cultural characteristics so Branagh decided to give his version of the story one black brother and one white brother. However, it’s the illegitimacy of the second son that is relevant, not his different skin colour.