How many books have you read where you had no idea what the characters looked like? Maybe the author neglected to mention it at all, or perhaps only once in passing, when the person was introduced.
Imagery is important in a story. Thus, it doesn’t hurt to remind readers what characters look like occasionally. One way to do so without being redundant is through action, such as “he raked his hand through his dark hair” or “her green eyes burned with passion.” That hits the “refresh” button in your reader’s mind without slowing down the story and is one example of “showing” as opposed to “telling.”
Another trick is to give your characters some outstanding trait. Do some people watching the next time you’re shopping or at an event for ideas. It’s been said that people who are too perfect looking are the least memorable. This applies to fictitious characters as well.