Colby is the toughest matchup for Usman in my opinion.
They are both very similar fighters. They are high volume, high pressure fighters. It's going to be a war of attrition between them I feel. It will be tough for them to take the other down, so it will mostly be fought on the feet with a lot of clinching up against the cage (where Usman has the advantage imo). Colby is a bit more active and will have a slight advantage in the center of the octagon based on volume, but Usman is more accurate. On paper I would give this fight to Usman, 3-2. If Usman gases then Colby can steal the fight.
Obviously hoping for Kamaru to finish the guy, but I see it going to a very close decision. So I'm going to say Usman by decision (either majority or split).