It's fun to ask them directly what compelled them to make the comment. In a neutral, non-antagonistic way. They shift around a bit uncomfortably, sometimes. Thinking. I enjoy that.
I get comments on being 'too pale' at times, and the same thing applies. I got tired of people telling me I 'needed a tan.' Yeah, I'll go cook my skin just to make you feel comfortable. Pff.
Some people will always find things to be critical about in unconstructive ways. The brat side of me just says, make them uncomfortable back by pointing out how obviously tactless/ignorant the commentary is, or if it were someone I cared about, I'd be more direct in analyzing/resolving that issue, though. Maybe they're projecting their own insecurities, & maybe asserting one's own self-acceptance can indirectly help them to do the same, over time.. if that makes sense.