You don't need a milling machine to install a colored front sight insert.
Any gunsmith worth the name can hand file a dovetail, and in fact, if you have normal manual skills most gun owners can do their own insert easily.
Here's my instructions on installing your own insert:. It's actually easy than it sounds:
First step is to cut a slot in the front sight were you want the insert.
If the sight is on the gun, use tape to thoroughly tape up the gun so there’s no chance of a missed file stroke scarring the finish or for a vise to scratch it. Leave only the sight exposed.
The trick is to get the slot toward the top of the sight so when finished and you look through the sights you don’t see any steel above the insert.
First, use the EDGE of a good, wide file to file a shallow slot in the front sight. Using the edge of the file makes it easier to keep the slot uniform and even since it‘s easier to tell if the file is tilted.
The slot doesn’t need to be very deep.
After you have the slot filed, get a triangular needle file and grind one side smooth. This makes a safe edge file, so you can file the undercuts without deepening the slot.
You can also buy a sight dovetail file from Brownell’s.
Use the file to file the ends of the slot to make undercut dovetails. These undercuts don’t need to be too deep.
Use the files to clean up the dovetail and make the bottom flat and the dovetailed ends even.
Buy a small drill that’s about half as wide as the sight blade.
Use the drill to carefully drill two shallow holes in the bottom of the dovetail. These holes were used by S&W and form “locks” for the insert to lock into. This makes a much stronger insert that won’t loosen or come out.
Make sure to use a center punch to mark the holes so the drill won’t drift off.
Use a solvent like Acetone or lacquer thinner to degrease the sight.
Make up two "dams" from small, flat pieces of metal or thick plastic.
Apply a coat of wax to the faces of the dams, then clamp them to the sides of the sight blade with a small pair of Vise-Grips to form a mold around the dovetail.
The wax prevents the epoxy from sticking to the dams. You can use Johnson’s Paste wax or shoe polish wax.
Mix up some 1 to 2 hour type epoxy glue. The longer cure time gives more working time and allows the epoxy to level in the dovetail.
After mixing the glue, put a SMALL drop of Testor's solvent-base model paint in the glue and mix it thoroughly.
You need only a very small amount, and the less you use the stronger the insert will be. If you use too much the insert will be weak and crumbly.
Experiment to find the right mix. Use just enough to color the glue properly.
Use a toothpick or needle to pack the epoxy mix into the holes you drilled in the dovetail, then use a small screwdriver or toothpick to put a drop of the epoxy-paint mix in the dovetail.
You want exactly enough to fill the cut to the top of the sight, level with it but no higher.
Brace the sight, (or the whole gun if it's on the barrel) so the face of the sight is level.
This will allow the epoxy to settle level and not run out.
After the leftover epoxy is like a hard rubber, remove the mold and use a brass or plastic "knife" to clean up any excess epoxy.
Allow to fully cure for 24 hours in a warm place, and you're good to go.
This home method works just as well as the commercial sets, and is considerably cheaper.
It's not really all that hard to do this with a little practice, and you can save some money.
You can practice filing the dovetail, drilling the holes, and filling the dovetail with epoxy by using the edge of some steel plate to practice on.
