I think self-inserts usually manifest themselves in terms of personalities rather than physical appearance, to be honest. I mean, I once drew a character who had brown hair and was like EWWWW that looks too much like me, but she was nothing like me as a person so realistically, that doesn't actually count as self-insertion. It's more about how you and that character relate on an emotional level - and to be honest, self-insert characters are a HUGE pet-peeve of mine. Oh yes, here's this mediocre middle-aged dude protagonist who inexplicably has sexy alien babes throwing themselves at him... I already know everything I need to know about the author just from that alone, and it's kinda gross.
So, since I have such a strong revulsion for self-inserts, I try pretty hard to not have them in my stories.
That being said, I'm not Ursula K. Le Guin. I can't write characters I loathe. So there is probably some emotional overlap/similarities between me and my characters, since I'm not a good enough writer to be able to empathize with someone who thinks completely differently from me (i.e. I can't write someone who's a racist, sexist, class-and-money-obsessed jerk unless that persona is fake and there is a more interesting human underneath).