This might sound kinda dumb.... but bear with me for a moment!
Have you tried a high quality lubricant like Break Free 'Collector'? I just happen to have recently purchased an Eagle Arms rifle, and experienced the same color situation as you have. I remembered reading a post about this fairly common complaint and followed the advice.
Took a piece of clean cotton cloth and rubbed in the oil and to my pleasant surprise it turned a nice matching black, and stayed that way. As an alternative to a refinish job, what do you have to lose? I'm not really sure if the brand or type of oil makes a difference, but this 'Collector' seems to hang around forever!