unique is a good powder for the 45 Colt. I shoot more Trailboss in 45 Colt than any other. Cowboy loads, but I would not call it clean burning. AA5744 is a good bulky powder that can duplicate original 45 Colt loads. I also use it for "Ruger Only" loads.
Your cleanest burning powders for the 45 Colt are the magnum powders listed in loading manuals as Ruger Only loads. Don’t shoot any of these in the Peacemaker or Peacemaker Replicas.