I've found the 'reset' thing a bit weird. Remember Tennant did it too sort of to heal his cuts and bruises for his goodbye tour
I've speculated BBC might have requested they wanted the Doctor to be in his "traditional" look for his final scene. If true, it could also have been a factor in why RTD abandoned his plans of dying Tennant's hair gray in TEOT to convey quite a bit of time had gone by for the Doctor since Waters of Mars.
Honestly, I'd have liked to have seen that. At least he might not have been so young by the time he regenerated.
Also, that brings to mind when they aged Tom Baker's Doctor for several centuries in "Leisure Hive", and the rumor that JNT wanted to keep that aged look for the Fourth Doctor until his regeneration, but TB refused. Understandably, although if he didn't object back then, imagine the possibility of an actually aged Tom Baker returning for a further anniversary? Very feasible, I'd imagine.
But its all academic, I suppose.