On this exact thread I've been served several adverts using models with beautiful dark brown eyes to try to sell me things.
Your feelings about yourself aren't wrong, because they're your feelings. And I don't agree with the PP who suggested that by disliking your own dark brown eyes for yourself, you're somehow insulting everyone who has dark brown eyes. We always judge ourselves differently to others.
But I think maybe it's something other than purely the colour of your eyes that's making you feel this way. There's nothing intrinsically plainer about dark brown than hazel or blue or green or violet.
Dark brown eyes can be very beautiful — I personally find dark brown eyes captivating on a woman, especially if they're so dark that it's hard to see where the irises end, and the pupils begin. I can't be alone in this, because there are many beautiful and striking women who get work at least partly through their looks and who have dark brown eyes. I'm sure there are other women with dark brown eyes who you wouldn't think of as plain, either.
I'd bet there's something else — a self-esteem problem, a half-remembered childhood insult, some other physical feature that's affecting how your eyes look (perhaps one that can be modified like eyelashes), a problem with your general mood, something that's making you pick on your eye colour as a problem.