Use yellow, or some other unused color to denote clusters occupied by unmovable files like the hiberfil, the System Restore Points, etc. Granted the pagefile has its own color but for other unmovable files it is confusing when you put their occupied clusters in red - this is not real file fragmentation since the Operating System has locked these files so that their clusters cannot be moved. It is misleading to see all that 'red' in the disk map when it does not represent clusters that can be moved and made contiguous. Competing defragment utilities do not portray unmovable clusters as 'fragmented': I think they got it right and would love to see Piriform follow suit.
Nice idea.