It sounds as though you look a bit different to the "norm" and that people with zero manners have, in the past, decided to take the piss out of that. This would upset me if someone did it to my family too - but I would hope that ANYONE invited to my wedding would have the grace and manners NOT to do that to my family member on my wedding day.
I imagine that she has suggested the hair and clothing change to try and minimise your unusualness, and reduce the chance of people being mannerless towards you, rather than trying to make YOU feel different, maybe?
But either way, this HAS to come back to this: have a conversation with your sister. A proper one, where you bring up the issues you have with it, and where you explain that you don't want her to deal with any side-effects of you being you.
And then if you're still concerned that people will be whispering about you during the ceremony (unlikely as you'll be near the front and most people won't see you) or the meal (potentially an issue, granted), then suggest that you come to the evening only. Or ceremony and evening but skip the meal.
I think you're getting an unnecessarily hard time here, but it is AIBU, so par for the course really - but I also think that you're also holding back what I feel are significant details that would more readily explain why you (and your siblings) feel the way you do.
Re. your eyes, maybe you could invest in a pair of coloured plain glass specs for the day, if it's something that bothers you/ your sister in terms of photographs? But only if you want to.
Talk to her, be open, honest, plain and direct. Ask her to do the same. Hope you resolve it. 