I was wondering this because I want to use a figure, senator Robert Kelly, to prevent opponents from ignoring pushing damage. I know indom/willpower count, but does colossal stamina count too? I know it doesn't use the word "pushing" anywhere in the entry for it, but it basically is a 2nd push. Grasping for straws, probably, but I just want to be sure.

No, it is not pushing damage. If your character with colossal stamina has indom or willpower it can ignore "pushing" damage, where colossal stamina is allowing you to attack/non-free action each turn at the cost of 1 unavoidable damage for doing so, after already have 2 action tokens on your character.

I don't believe so but I'll try to get you a quote.

"Basically" doesn't cut it. Pushing damage is pushing damage. Nothing else is pushing damage.

Using Colossal Stamina causes the character to take unavoidable damage, though, so barring old-school Colossals like Galactus and Spectre (which specifically state they take no damage) or the occasional AoU Hulk, there is really no way to NOT take the unavoidable damage from Colossal Stamina.

COLOSSAL STAMINA
character automatically breaks away and can use .When this character has two action tokens, it can be given a non-free action. If you do, after actions resolve deal it 1 unavoidable damage and do not clear action tokens from it at the end of the turn.This ability can’t be countered.

No where does it say push