Please check the Help which describes this:
https://www.hdsentinel.com/help/en/61_surfacetest.html
Darker green color means that the sectors are slower and harder to process.
As these sectors are still readable, good (you may notice the counter of good/damaged/bad blocks on the right, next to the disk surface map) there is no indication of problems: the drive is NOT failing at all and as the sectors are good, there is no need to "fix" these darker green areas.
The Help (see the bottom of the above link) shows some examples about disk surface maps.
Usually some darker green blocks are completely normal and expected, sometimes the OS and/or other background apps can cause this (even if Hard Disk Sentinel does everything to minimize such effect). If they appear randomly, there is usually no problem with them.
If they form a continuous large area and there may be yellow/red blocks near, then the slower performance may indicate coming falure / damage in these blocks too (there is a such sample image on the link and in the Help).
Then yes, the Disk menu -> Surface test -> Reinitialise Disk Surface test can be used to force the hard disk to re-test these sectors, repair problems by re-allocation of sectors (if required) and in many cases then the performance increases back (so a following read test shows no or fewer darker blocks).
If the drive may have/had other problems (you wrte that bad sectors fixed during the test, so I assume the drive was not perfect, not 100%) then yes, personally I suspect I'd run a Disk menu -> Surface test -> Reinitialise Disk Surface test to make the drive "fresh" if possible.
But generally if the health of the hard disk was 100% and only darker green blocks appear - it is not required.
