Both are lovely!!
For the Jewel Box ...
My first thought was thinking a motif (flower, star, whatever) in the center square, SITD around the border diamonds and do a small stipple (or other dense quilting such as pebbles, or ripples) in the dark part to make the colored sections stand out. But I also like the pattern that Katier pointed out for the jewel box.
For the other one ...
I'm not getting as clear of a picture in my head ... I'm seeing feathers in the light areas surrounding the center square but not sure how .. wish I could be of more help. I really like this one, it sparkles!!