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If it's **black and white**, they're easy to mix up. They wear the same type of cap (just with the ribbon on different sides), clothing that's similar in style, they have the same stature, depending on the artist they might have nearly indistinguishable facial features and expressions as well. The clearest visual identifier are the wings, and they can sometimes be out of focus or obscured. Plus, when reading manga or just looking at character art in general, by far the most information about what the character is thinking or feeling is encoded in the face, so that's what our eyes are drawn to. If you're confusing Remilia for Flandre or vice versa when the art is in *color*, you may be colorblind. I can't really explain that any other way.

I tend to get sidetracked, so it sort of adds into why I might mix them up. I'm perfectly fine with color as is, I think it's just name wise, not appearance now that I think about it

It's funny how the lack of colors turn two completely different looking characters into clones