Ran Slimbuild of Defraggler 2.14.706 on WIN 7 (64bit) to perform quick defrag. Although fragmentation is indicated as zero, a pink/light red square remained. Could not find any fragmented files corresponding to that square. I expected all squares to be blue, except for the 'swap' file in beige.
My understanding is the coloured blocks are not perfect.
They are a guide.
If you adjust the border to give the file map as much screen space as possible, you will get more blocks per file ratio and it may give you a better picture. And crank up the monitor resolution for this exercise to further improve your block count.