I'm the same, it wasn't Mum who did it - it was a pet peeve of hers too, but it was Nan and my Aunties who used to buy my cousin and I the exact same clothes only in different colours for Christmas we were only 6 month apart and I hated it!! I vowed never to do it to my kids LOL. Also because I was bigger than my cousin it always looked crappy on me, but great on her so that was another reason I turned off it. I can't do it to my girls even if I wanted to because of their colouring. DD1 has slightly fairer skin and lighter brown eyes so pastels suit her better but DD2 is darker with darker tones and darker eyes so she can wear really bold, bright colours.

LOL at the Mummy-Daughter twins though - I know two woman who do that with their daughters and it creeps me out - their clothes are nearly identical and the one with the older daughter is worse because the DD is around 19 and they even dye their hair the same colour and wear it in the same style

Nickle, at home it is trackies all the way and often they will wear similar looking clothes, but for 'good' clothes I avoid it at all costs.

RhiChiChi - you need to check out awkwardfamilyphotos - another good reason to never dress your kids in the same clothes LOL
I'll definately check out that website

In relation to the hair thing, a mum that used to be in our mums group gave her DD the same haircut as hers...... it looked awful. Not b/c they were the same but b/c the haircut was horrible.....:S what was she thinking....

We got family portraits done a couple of years ago, and I dressed my 3 girls in the same white shirt, and the 2 older ones had matching skirts. I think the photos are beautiful, and don't think myself a weirdo for having dressed them that way.
My older 2 have a few items the same, but they tend not to wear them at the same time.
I don't think you are a weirdo - it's just personal choice. Having said that though, DH step-siblings got a portrait done of all of them (there are 7 of them) and they had black or white t-shirts & jeans, which actually looked good.