Rear sight dots are over rated and I have used them on various pistols for about 3 decades. Your focus is the front sight, a black rear sight makes it easier for me to focus on the front sight. The 659's front sight is milled as part of the slide, so no easy way of changing the sight, but you can paint the sight. A base coat of white hobby enamel (Testors) followed by a couple of coats of fluorescent hobby enamel (I like the fluorescent green) might work well for you.
Alternatively, if you don't mind a sight picture that looks more like a bullseye target pistol, paint the front sight in matte black hobby enamel. If you want to go cheap or just experiment with a black front sight, use a permanent ink black magic marker/Sharpie pen. The ink is easily removed with just about any solvent.