It's hard to tell about that...she certainly favored black in her later years, that much is apparent. The emeralds...the emerald jewelry that Elisabeth had was a gift from Franz Josef, I'm pretty sure, and who knows if he knew her favorite color! Surviving dresses of the Empress's are black, of course, lavender, white and pinkish...I can't recall that I've seen any other colors. Garnets as well as rubies were in her jewelry, I think, but her color preferences can't necessarily be judged by her jewelry unless she commissioned it herself...lots of it likely were gifts.
This portrait by Franz Schrotzberg (spelling??) could be a good hint. I read that she posed reluctantly for most other painters, but apparently not for Herr S....so she might have chosen her clothes here...
Black lace, pale pinkish white and sky blue...
This is just a wild guess, but perhaps as a young teenager in Possenhoffen she liked green...because she loved the forest, and riding and being in the wilderness. Of course when she became Empress, Elisabeth was bound by all that court regime that she so hated and as such she mightn't have been permitted to display much of her favorite hues...
As for flowers...Violets do sound fitting. Where did you read this, Rani?