Yep, he's fully metal, even though he retains his organs and innards, everything is organic steel. There's literally nothing T-1000 can do to Colossus, while Colossus can just toss T around and splatter him over and over again, eventually the matched will be called due to TKO, or the fact that one of the fighters can't do anything to the other. It's like Thanos against Squirrel Girl.....The Real Thanos.