I agree with the others. If you're not going to match exactly to your applique fabric, I would go with a 100wt silk & buy white, charcoal grey & cream. Those 3 colors would blend in the best.
Depending on what colors you prefer, Aurifil (my personal favorite since I like 100% cotton quilts) does sell thread kits with coordinating colors. As far as what is the "most common", it depends on what you like to quilt. Baby quilts might use a lot of white/pink/blue/green/grey. Kids' quilts might use more primary colors. If you like doing Baltimore album quilts, those are often darker tones. One tip I would share with you if you're going with cotton is to buy the small 200m spools of Aurifil. Hawthorne Threads has the entire Aurifil collection available on their site & I'm always happy with how quickly they arrive.
http://www.hawthornethreads.com/threads/aurifil