Fingernail acrylic can be used to cast inserts into the dovetail, and something similar is what gun makers use.
You can also use one hour epoxy and a very small amount of model car paint to color it.
This requires some experimentation...too little and the color is light, too much and the epoxy gets crumbly when cured.
Inserts can be made from solvent proof plastics like toothbrushes, but my favorite is brightly colored cheap screwdriver handles. Many hardware stores have a basket of cheap tools and often you can get good colors for a buck or two.
Making the tiny insert requires some very finicky hand work.
Any gunsmith worth the name can do it for you.
An insert doesn't have to be ref or orange.
Here's one in a S&W sight. I installed a Black insert then carefully ground in a very shallow White oval. From the rear it looks like a round White dot.
With a White bar painted under the rear sight notch I have a nice Von Stavenhagen sight.
When casting or gluing in a solid insert, fill the holes in the bottom of the dovetail. That forms a "lock" to prevent the insert from ever coming loose.