We used to paint everything in the Marines, either with spray or by hand, inluding the old Unertl scopes. I'm not sure what kind of paint we used because it was in plain packaging with an NSN number. It looks good at first but it will chip after some field use. If you go that route here are a few tips from a class on painting a scope. I can't remember what website posted this originally so I don't have a url. MATERIAL. Lens paper and tape are the only materials necessary. Any solid tape will work. Masking tape is preferred. The reason for this is that it doesn’t leave any residue behind and can be torn by hand easily if no sharp instrument is on hand.
SCOPE
a. The scope is broken down into two groups. The first being the objective and viewing lenses. And secondly, the elevation and windage turrets.
1) OBJECTIVE AND VIEWING LENSES. These must be covered so as to protect the coating on the lenses and so viewing remains unobstructed. To do this, you must cut a piece of tape large enough to fit over the lens. This maintains a paint free lens. Before applying it to the lens, you must fold two to three pieces of lens paper and insert them in the lens well. Then apply tape. After it is applied, you may trim it.
2) ELEVATION AND WINDAGE TURRETS. These must be covered to protect the rubber "0" rings that waterproof the turrets. Also, the numbers on the turret must remain clearly visible and the turret easy to move. To do this, cut a strip of tape to completely encircle the turret, making sure that it covers to the outer edges of the numbers and includes the "0" rings. You must also cut a 1/4" x 1/4" square piece of tape to cover the allen screws. This ensures smooth and easy operation of the screws and allows you to properly zero the rifle.