Ninja changes since first idea (but before posting)
General - Health regen per level reduced to .7 from .8 to better match averages.
General - Mana regen increased from 4 to 6 to better match averages.
Neverrun (Q) - Now only bonus damage can crit.
Neverrun (Q) - Range increased from 500 to 650 to get as close as possible to the intended range (I grossly overestimated the range).
Colour Shift (R) RENAMED to Rebirth (don't deny it. Colour Shift is the most shitty name possible...)
Rebirth (R) - Now costs 40 mana from no cost.
After post edits:
14 May 2013:
Rebirth (R) tooltip updated to mention that Tha'vor's colour changes depending on the amount of charges he has. His colour without a point in ult is red.
Rebirth (R) - Now costs 75 mana up from 40, to add more need for mana management.
Neverrun (Q) - Tooltip now states it procs on-hit effects in addition to critical strikes, as is how it's meant to work.