It is my understanding from reading this section of the regulations that it is illegal to have any sort of sighting aid or magnifying lens on your bow. That is the same interpretation that I have heard from CO P&W game wardens.
." Scopes and electronic or battery-powered devices cannot be incorporated
into or attached to bow or arrow, with the exception of lighted
nocks on arrows. Recording devices such as cameras or video recorders
attached to bows may be used as long as they do not cast light
toward the target or aid in range finding, sighting or shooting the bow"
The justification for this is similar to the Muzzle Loader regulations not allowing scopes. Their goal is to keep the Primitive Weapon seasons as primitive as possible. "k. Only open or iron sights allowed in muzzleloading seasons. Fiber optics
and fluorescent paint incorporated into or on open or iron sights
are legal. Scopes or any sighting device using artificial light, batteries
and electronic gear are prohibited during muzzleloading seasons."