I have always wanted to make one of those quilts...It looks great!
I think I am out voted but I would go for charcoal grey....At least on the top....the back could be anything.
I think I agree with you Charismah. The quilt is busy enough as it is. Everytime I have used varigated thread I have regretted it. The Tone on Tone threads are really nice though.
If you can get your hand on Invisafil thread, they have some beautiful solid colors that will just blend in and not overpower the piecing. Nice quilt. Love Bonnie's patterns.