Cream and white might wash up close to the same, but speaking from experience, cream shows less dirt in the meantime, so I think your idea is a good one.
This is just a thought Ally: Since you will be replacing all that background fabric and the kit is small for your bed, perhaps you would be better off just buying the digital pattern and choosing your own fabrics. Kona cottons are a good quality solid fabric and you can purchase their color chart and use it as a pallette to chose which colors you like best with the cream:
http://www.robertkaufman.com/fabrics...ton/#colorcard
I love the color card - the fabrics stay in stock for a good long while and you can count on the color being accurate. It's saved me a lot of shekels in the long run.