Not a hand quilter so I can't tell you if pebbling or meandering is a good idea to do by hand. I can say though that pebbling is typically done with pebbles in varying sizes.
Personally ... I like Barb's idea of running a cable or braid up the white strips!! That will give you more quilting than just the single line that is shown. It's a fairly easy pattern both to mark and to quilt - but has a lot of punch to it and will make those white strips sparkle. You can use either white or purple thread to quilt.
As for the colored blocks ... you can either treat each colored block separately, or treat the whole colored "stripe" as a single item (in which case perhaps a matching cable or braid quilted with white thread?). Another good choice to work either as single blocks or the whole stripe would be clam shells which would compliment the cable/braid.
I personally would not use an all over design for the whole quilt. I would treat the colors and white as separate items and quilt each accordingly.