Scotchbrite,,the maroon or gray colored pads will leave a nice finish.
A fine wire wheel will make quick work of it. Coat the surface with oil first and use light pressure and you'll have that nice 'burnished' look.

Any chemical that removes bluing will remove case colors. But disassembly, dunking, rinsing, oiling and reassembly is required.

The others are less messy and time consuming. You can leave colors on the inside and protected areas with them too if you want to.