<human>: Can you succinctly summarize the text in 1-3 sentences?

I am getting married in 6 weeks, my sister is one of my bridesmaids and has just unveiled a new do. She coloured her hair a pretty bright shade of purple. It looks pretty good, not a muddled colour or uneven however I am worried about it clashing for the wedding (our colours are coral, fuchsia and green) and standing out in the pictures. 
I haven't talked to her about it but my mom mentioned something about her changing it for the wedding and she was immediately defensive. My sister and I haven't always gotten along and I like to avoid confrontation with her as she can be quite angry and stubborn.  
My fiance says I shouldn't worry about it, that it's not a big deal and that I'm just stressed out. . . 
I know it is her hair and I guess what I want to know is whether or not my concern is valid and if so, how do I approach talking to her about it?
<bot>: My sister (bridesmaid) is going to have purple hair for my wedding, can I ask her to change it? How?