Stand up to her. I was raised to respect my elders, however sometimes there is a line. She has no right to be insulting just because she is an elder. You can kindly say something like "I was raised to respect my elders, but Im very close to crossing that line with you." Or flat out ask her why she is insulting you all the time. Sometimes when someone is faced with having to explain themselves, they can't and realize they better stop, or she'll respect you more for not dealing with her crap. Tell her you just like green but you like all colors and if she is inclined to buy you a gift ever, any color she wants is fine with you. Mothers! LOL (Kidding!)
