Try washing them with tooth brush. If they don't brighten up, you might get them replaced by S&W or the manufacturer. Three years is awful quick to fade, they should be under warranty.

Novak Sights offer a good selection.

You have a rock solid gun, easy to shoot, low recoil and reliable. They are a bit heavy. A good belt and holster are a must, look at Ritchie Leather.

I've had my 4586 for 24 yrs, still shoots great.