This is more likely the result of generous chambering than load issues. 45 Colt chambers are notorious for being big. At ignition you get powder started out of the case and then ignition. The case has not fully expanded, so you get combustion residue around the case mouth and farther down.
If the firearm that you are loading for will take a slightly higher charge, that may help. The tighter crimp might help. But if you are loading only for this firearm, don't full length resize. The case has now expanded to chamber size, so only size the case mouth for bullet seating. This will limit the amount of free space available in the chamber for combustion. Lastly, experiment with slightly longer bullet seating if possible. It's counterintuitive, but seating the bullet slightly more shallow can also reduce combustion residue in the 45 Colt.