With S&W, the aftermarket choices for a white-outline rear sight are small. Millett used to make a rear sight assembly with a very high visibility outlined rear blade, but Brownell's, the gunsmith supply house where I go for such things, is showing the Millett as "Discontinued by the factory."
Originally Posted by nvdesert
Brownell's can sell you an entire S&W rear sight assembly for about $68. All you'll need to do is loosen and remove the tiny mounting screw, slide the sight rearward to remove the elevation nut from the slot in the frame, and repeat in reverse order for reassembly with the new sight.
You can also get kit to replace the sight blade only for about $17-$23 (depending on shipping costs). To replace the rear sight blade on a S&W revolver, you have to actually break the windage adjustment screw, because the end of the screw is riveted into the nut during assembly. It's not terribly tricky, but there is a risk of getting the sight too tight or too loose in the sight body, with associated problems of binding or excessive side-to-side movement. There is also the possibility of bending/breaking the screw during the riveting of the nut. Any competent gunsmith could do it, but after you pay him to do the installation job, you probably could have bought the entire sight assembly for less money, and had the old sight assembly as a backup, too.
Here are links to Brownell's pages for the sight assembly and the rear sight blade kit. Important note: both of these items are offered in various blade heights for different barrel length revolvers, and if you get the wrong height, then you will be WAY off target when you try to shoot. These are examples, but not necessarily the exact heights you will need; to find those, you'll have to measure your current weapon's sight blade height.
"Placement is power" -- seen in an article by Stephen A. Camp
(RIP, Mr. Camp; you will be remembered, and missed)