If you don't want to use white, use grey.

Antique White is always a good fall back. What I usually tell people to do is take your tile samples, and put multiple grout samples with them. Blur your eyes to see which one blends the best. With your colors you may even want to consider a very light grey with a greenish under tone (because of the pistachio).

I would definitely go with a light gray of some kind. I think it would go very well with the green and, well, it's not white. :)

There are several different colors of white grout available. We recommend taking a sample of your tile to a tile showroom and comparing with the different grout samples. Good luck!