Yes, I've seen this many times. Many Parkerized barrels have three colors. Sometimes the barrel mounting ring is silver and/or purple.
I don't know a whole lot about the Parkerizing process, but I've been told by the folks that do that time, temperature and the type of steel all play a part in the finished product.
I have noticed that some barrels seem to be harder from the lug to the muzzle. This may be due to the brazing process. This could be why you see two tones.
Of course, I could be full of ...........