I love purple and green together! You have a light green and a dark green --- try to throw in a few medium greens. Both of the purples are on the dark end --- adding a few mediums and a light purple will keep the quilt from looking "heavy" or "flat". Does that make sense? Try to avoid checks, stripes, or anything else that has a directional pattern---- the small florals and wavy patterns are a good choice. :D
Do you have a design board to work on? They really help a lot when you are making color choices on a pattern like this one.