Appearances can be deceiving. For instance a handsome hunk can be a jerk. Or a chunky nerd can have the heart of a knight. Too often we don't really look past the outward appearance to really see what's underneath. One of the nicest men I've met in my life was a school teacher that taught building and construction. He was uglier than sin on the outside. But on the inside he was pure gold.
A reader once wrote to me to tell me that she liked my secondary characters because they were "real". Had to think about that for a while. I think she might have been talking about this appearance thing. Books can't be filled with only beautiful people without setting the teeth on edge. It's kind of like having too much sugar in the fudge. It just makes your teeth ache.
It's best to temper that with what I call medium...medium coloring, medium weight, medium height...medium. So your secondary character Joe is not too tall, not too short, not skinny, not fat, with brownish hair and eyes. That's pretty much most of the people around us. There are other variations out there.
The neatest trick is to then let that individual be your villain. They're perfect. No one will suspect them. That's the beauty of appearance. If you are skillful enough at camouflage to be invisible, then the deceit is complete. And shocking. After all, isn't that what the neighbors always say about the killers? He was so ordinary.