Comeuppance’s effect is not a redirection effect. If it prevents damage, Comeuppance (not the original source) deals damage to the creature or player as part of that prevention effect. Comeuppance is the source of the new damage, so the characteristics of the original source (such as its color, or whether it had lifelink or deathtouch) don’t affect the new damage. The new damage is not combat damage, even if the prevented damage was.

If Comeuppance would deal damage to an opponent, you may redirect that damage to a planeswalker that player controls.