from Nasa;
http://www.nasa.gov/jpl/dawn/dawn-sp.../#.VNyA3fmUexU
"Ceres, in contrast (to Vesta), has a thick ice mantle and may even have an ocean beneath its icy crust."
the circular white areas do look like craters and as the surface is ice, i reckon the brighter areas must be 'cleaner', and the brightest - the cleanest ergo the newest??
NASA says "All we can predict with confidence is that we will be surprised." bring it orn!!
Lindon