When I got married I wanted a pale green for my bridesmaids, but my mil objected saying it was unlucky. Never heard that before.
I went with peach in the end.
I bought a dress with a green, cream and grey mix pattern (it was lovely) and a matching green jacket for my brothers wedding. When I showed my future SIL it (too late to return) she was horrified so I just wore a black and cream dress which I already had but didn’t feel confident at all.
So wear what makes you feel good!
People who believe in faerie myths will think it an unlucky colour. Think of the tale of the Green Knight in the Arthur/Camelot yarns. Rational folk know better and wear whatever pleases them.
The only reason now I won’t wear green and think it an unlucky colour ( for me anyway) I did a zip wire from 850feet up , dressed in green, tights,skirt top and a cowboy hat on St Patrick’s Day two years ago in a blizzard.....then tripped over a snow covered 3 incH kerb when I came down, smashing my specs and getting two lovely black eyes , now I won’t wear anything at all green :0/
The only consideration I'd have colour wise would be how strong the colour was, basically that it wouldn't stand out like a bit of a beacon in wedding photos, but that goes with any colour. Never heard of not wearing green to a wedding. I have in the past, a gorgeous silk patterned skirt in different shades of green and a darker green top, both from Monsoon.
Just re-read the question, is your sister the mother of the bride? If so is there some issue over colour schemes for the bridal party (more bridesmaids maybe) or clash somewhere colour wise?