Very tough - SureFire FM35 Red Filter for flashlights with 1.25" diameter bezel (Z2, C2, C3, G2Z, G2, 6P, 9P )

Expensive, but built like a tank. The picture is a bit misleading. It is only red. The bezel actually has a friction clamp to hold the whole thing on. The only complaint I would have would be it is you are not going to be able to switch between red and clear if you have gloves on. There is a very small locking lever that has to be opened to flip the red lens over.
Pros: Not going to break it. Very heavy duty
Cons: expensive

This review was written in the old system and had content requirements that are different than reviews written today.