I don't think you're being unreasonable at all!
She likes wacky hair, yet dyes her hair a normal colour for her own wedding. Then for your wedding she waits until she knows the colour of the dress and then dyes her hair to match it?! I'd be a bit
. So it's important for her wedding to have nice photos, but not yours?
That, to me, says she doesn't have a very high opinion of your wedding. It also kind of says that she thought her wedding was far more important than any other wedding, especially if it takes place after hers.
I have a sister who is determined to outshine me in every way, but she is so obvious and underhanded about the way she does it that it normally backfires on her. The last time she tried to be "number one" it split the family up and we don't even mention her name in conversation because we've all had enough of her and her "me me me!" attitude!
And even if I were on speaking terms with her, do you think she'd come to my upcoming wedding?! Not a flamin' chance. She'd turn up 8 months pregnant and wearing that godawful black wedding dress from the Hollyoaks advert, complete with dreadlocks, KISS makeup and a packet of fags just so she could cause controversy and make a splash.
I think that if she hasn't changed her hair by April 1st, you tell her that either she dyes her hair a normal colour or she isn't in any pictures taken by the professional photographer. Those are her options, take them or leave them.