First thing I think I'd do is add a few more dark colors -- darker blues perhaps -- and a few much lighter values as well. You are totally in the medium range of value here, with little contrast except the difference between the colors themselves. Usually a quilt will sparkle more if a wider range of values is used.
Your values of color don't have to actually *be* in the print you are using as your focus fabric, just use much lighter values of one or two of the colors in it.
Beyond that, stars using the various tonal fabrics would give a celestial feel to your aliens. Cute fabric!
Jan in VA