YIKES!I've heard that it has to do with the silicone content in Ruger's steel alloys for their blue guns. I've never seen it before on a DA Ruger, but it's pretty common on blued Blackhawks. I have not seen it on Ruger rifles or .22 autopistols, but I could have just missed seeing any that were affected.
This is a big reason why I buy stainless Rugers!
You can have the gun plated, probably in hard chrome. If well done, it will closely resemble stainless. But be sure to know who's doing it and be familiar wth their reputation.
Unless the gun has great sentimental value, I'd just sell it to someone who isn't bothered by the color and put that money into a good stainless example or a GP-100. But most people will chisel you on price because of the plum color and you'll take a beating. May be cheaper to have a competent house plate it, and the gun is a known quantity to you. You know where it shoots, with which ammo, and the size is handy.
On balance, if you have adequate funds, I think I'd plate it. It isn't cost effective, but it will get you a fine gun. Money is just money. A good gun that you really like is something more.