My first thought in response had nothing to do with twins. Long ago, my own mother had a friend, a sweet lady who had lovely clothes and wore almost every color except blue. She said once that her mother was convinced that blue was best for her, and EVERYTHING she wore as a child had to be blue. So when she grew up she never went near the color again.
I don't see why your twins can't wear non-identical outfits. Jane is Jane and Susan is Susan, even if they look like clones to the rest of the world. Do they ever ask you if they can dress alike?
My two girls were not twins but were close in age. Occasionally I dressed them alike when they were little - and occasionally they didn't mind. They looked darling, if I say so myself. It's not the style these days to do that - the trend now is to let children choose all their clothing for themselves.
I'm sort of in the middle about it. I liked the idea of my children (both girls and boys) being able to make choices most of the time, but I tried to make sure that their choices were good ones, and I tried to teach them about the differences between winter and summer clothing, what looks good together and why, and all that. It can be a good teaching opportunity without cramping anybody's style.
Oops - I need to make an exception to that. When a photography session was going to happen, then the children were told what to wear, and often they dressed alike, or were at least coordinated. But that comes under the heading of costuming.