Ruger has reblued a few for me, all under warranty. However, there was always an underlying issue that required the reblue.
A .44 Super Bisley with chatter marks in the rifling. Replaced barrel and reblued gun.
A .357 with burrs in the cylinder window. Repaired and reblued the frame, but not the cylinder.
Most recently, I sent in a New Vaquero with the case color frame. It has a broken off grip frame screw, caused by the PO. I also mentioned I hated the billboard barrel and requested an estimate to replace it with a newer barrel. They sent the gun back within a week- screw repaired, new barrel installed, and barrel, cylinder, and grip frame mirror polished and reblued. All for free. I did specify that I wanted to keep the case coloring.
Ruger reblue jobs are first rate. When I checked a few years back they were $130. I'm sure it's gone up since then.
By the way- the case coloring can be "touched up" with artistic application of a "quick blue" pen. Ruger's case coloring seems to be varying shades of grey, so a dab or two of the pen and then rubbing it off with your finger imitates the factory finish nicely.
Edit: looks like it’s still $130. I just copied this off their website.
I would also pay them for a shipping label. $45 and Fed Ex will pick it up and when it’s done drop it off at your door. Well worth it.