Individuality

(AKA that pony probably used to be blind or something. Or she's just really unobservant.)

& that's why Moondancer's glasses are taped up.

I couldn't think of anything else.

Update: I forgot to put "That pony has the 'you look alike except for your colours' conversation a lot." here.

Also: Featured on Equestria Daily 7/5/15. I don't need you, bot.