I am finding the current rating label style in thumbnails a little hard to read at a glance, in part because the rating colors are not distinctive enough.
I wish XN could display rating in thumbnails (and preview overlay) the same way as Adobe Bridge: no color, just the appropriate number of stars. I think it is a much cleaner, easier to understand style. From the UI design perpective, I think the eye/brain registers the number of stars more than the bit of color placed on one of them.