Unless the topic of skin colour is relevant to the character, then why mention it?
This was always my thinking, too, Thundering. I always thought, "Let the reader put him/herself in the place of the character. If I identify any physical characteristic, that will automatically leave out so many."
But too often, the default in readers minds is to make characters white. And that automatically leaves out so many. Yes, even if skin color is not mentioned at all. That doesn't represent the world that we live in .... and it's sad (and maddening and frustrating) for kids who are not white to look for books and see themselves in 1 out of 1000 stories. Think of dolls, from baby dolls to Barbie, to GI Joe, and how impossible used to be for parents to find a doll that looked like their daughter/son. Also, it used to be that publishers would whitewash covers, even if a character were explicitly asian. We had a Blueboard member who had this happen to her book. Why? The publisher thought an ethnic cover wouldn't sell. And that's not right. It took writers, artists, and editors speaking up for changes to BEGIN to happen, and it has been and continues to be a tough fight.
So I agree that plot is a crucial element of our stories. Of course it is! But so is representation of all the children we write for. And it's just as important that the writers and artists who get contracts are not just white men and women.
In my current book I mention skin color (of each main character) briefly ... and I tried to do it in a thoughtful way. Was skin color part of my plot? Nope. Not at all. They were three kids (two white siblings, and their black neighbor/friend) who were different from each other NOT because of their skin color, but because of their personalities, their fears, their confidences, their desires, and their quirks. In another story, maybe these kids would address skin color somehow, how it impacted them, but not this time. I wanted to write a story first -- a fun story where skin color wasn't the issue. My characters were too were busy dealing with all the other stuff I was throwing at them, LOL. But I don't live in an all white world and my characters shouldn't either. And it's my intention to help representation get better as best I can, as responsibly as possible.
Not everyone will agree with me. We all are coming at this from different places. I certainly think differently now than I did ten years ago . . . and I hope that my thinking on this subject will continue to advance and hopefully get better. We'll see!