The immediate questions that come to mind are: How long has Simmons been re-bluing Winchesters? And how long did it take for factory bluing on Winchesters to take on a purple hue? If this process takes several decades, it may come to pass that even Mr. Simmons jobs will turn as well.
I just read a tip from Brownell's Gunsmith Kinks II that recommended a process of putting nickel steel parts in the bath at 250 degrees, running the temp up to 310-315 for 15-20 minutes, then dropping the temp to 285-290 for another 15-20 minutes. I have also seen other variations on the process in other gunsmithing books. But none has addressed the issue of whether the color will stand the test of time. For most of us, 30 years will be more than enough. My Mauser 66S receiver was slightly purple when I got it around 1990. It was around 25 years old at that time. I think it is a bit worse now, but the change would be so gradual as to be barely noticeable.
I think rust blue colors can and do change. Most Damascus Lefevers that started out as black and white are now more of a purple/brown patina as the oxides have partially or completely converted to another form of rust. Plenty of other rust blued guns exhibit similar change in color ranging from near original blue to rusty brown, and everything in between. You could argue that the cause is neglect, or you could accept that further chemical reaction has occurred from exposure to humidity, perspiration, various oils, dirt, blood, etc. In that sense, I'd bet even well oiled closet queens would show some minute color change if you could compare the color by spectroscope over many decades, because some small amount of oxygen is going to get to the bluing through the oil over time. Very few of us store our guns in sealed vessels of dry nitrogen.
