I had a Dior bag in white lambskin in the past. I had to have it when I saw it because I thought it was so beautiful. But, when I had it, I was afraid to use it so at the end I sold it.
So my vote is for caviar as well.
Caviar. Light color + caviar = less maintenance & less prone to color transfer. However, I would not recommend getting a white Chanel. White Chanels are gorgeous but it will eventually turn yellow (as per the Chanel care booklet).
ETA: Do you think your sis will like beige instead? It's just as gorgeous but with fewer maintenance issues.
Wow... U r soo sweet...
It depends on how she is planning to use it and does she has any kids? If it is going to be a daily bag, caviar is the better option. Though Lambskin is more soft and gentle-looking. If she has children, def CAVIAR!!