Map Legend

The legend does not tell what the Light Blue or Gray blocks are!

The legend does not tell what the Light Blue or Gray blocks are!
There are also light red blocks which are not listed in the legend.

I'm pretty sure that the lighter colors mean that arbitrary chunk of the hard disk is not completely full. The gray boxes, assuming they are the same as the white ones on mine, are the empty parts of the disk where nothing is written. I could be wrong but that makes sense to me.