I don't find any prohibition for illuminated reticle on scopes for Colorado Big Game hunting.
Closest I see is "Smart Rifles" and a linked (? my guess) ballistics computer.
CO Regulations
ARTICLE IV - MANNER OF TAKING WILDLIFE
#004 - AIDS IN TAKING WILDLIFE
D. Smart Rifles
1. All firearms used to take or attempt to take wildlife shall be fired only by humanly controlled, manually-operated mechanical triggers. No person shall use a smart rifle to take or attempt to take wildlife.
2. "Smart Rifle" means any firearm that is equipped with one or more of the following:
a. A target tracking system;
b. An electronically-controlled, electronically-assisted, or computer-linked trigger;
c. A ballistics computer.
#203 - MANNER OF TAKE
A. The following are legal methods of take for all species and seasons listed in this chapter, except as otherwise noted. Any method of take not listed herein shall be prohibited, except as otherwise provided by statute or these regulations:
1. Rifles using center-fire cartridges of .24 caliber or larger, having expanding bullets of at least seventy (70) grains in weight, except for elk and moose where the minimum bullet weight is eighty-five (85) grains, and with a rated impact energy one hundred (100) yards from the muzzle of at least one thousand (1000) foot pounds as determined by the manufacturer's rating, and except for mountain lion where any center-fire rifle using bullets of at least 45 grains and producing at least 400 foot pounds of energy at the muzzle may be used. Provided further that any semiautomatic rifle used shall not hold more than six (6) rounds in the magazine and chamber combined. A fully automatic rifle is prohibited.
2. Muzzle-loading rifles and smoothbore muskets, provided the minimum caliber shall be forty (.40) for all big game except elk and moose when hunting with conical bullets and fifty (.50) caliber when hunting with round ball bullets. The minimum caliber for elk and moose shall be fifty (.50) when hunting with conical bullets and fifty-four (.54) when hunting with round ball bullets. All muzzle-loading rifles and smoothbore muskets from forty (.40) caliber through fifty (.50) caliber must use a bullet of at least 170 grains in weight. All muzzle-loading rifles and smoothbore muskets greater than fifty (.50) caliber must use bullets of at least 210 grains in weight.
a. During the muzzle-loading firearms seasons for deer, elk, pronghorn, bear, and moose only lawful muzzle-loaders and smoothbore muskets may be used by muzzle-loading license holders.
b. During the muzzle-loading firearm seasons for deer, elk, pronghorn, bear, and moose the following additional restrictions apply: Propellent/Powders: The use of pelletized powder systems and smokeless powder are prohibited.
2. Projectiles: Sabots are prohibited. For the purposes of this regulation cloth patches are not sabots.
3. Loading: Firearms must load from the muzzle. Firearms which can be loaded from the breech are prohibited.
4. Sights: Any muzzle-loading rifle or smoothbore musket with any sighting device other than open or "iron" sights is prohibited. 5. Electronic or battery-powered devices cannot be incorporated into or attached to the muzzle-loading firearm.
