Any red covering will do.
Jay (Outlaw) used plastic from a brake light repair kit to cut out a red lens that fit his flashlight.
I thought dogs, coyotes and wolves where all color blind and can't tell the difference between red and green.
Your above statement is correct, but I believe that red fox can see some color, that's why wearing blaze orange is not required in NJ while hunting fox and coyote from a stand.
As to the color,it's not really the color that is the issue, but the light intensity is a serious factor to consider.
When hunting predators it is recommended to keep the animals eyes glowing in the "halo" created by the light beam, and not directly in the beam. This will minimize scaring them off.
Also, your night vision becomes a factor. Most lenses leave gaps on the edge that spill white light out the sides. The spillage of white light is a bad thing as it fouls up your night vision and lights you up as well. However, it is necessary so the spotlight doesn't overheat and melt the lens.
To remedy this you can put a cowling on the light so the lens is recessed. This allows the cooling vents to remain open but keeps the white light contained. Modifying a black, plastic flowerpot works great.
Red lenses seem to work better for night vision than the green lens which seems to emit a "brighter" light beam.
FYI - Different animals eyes reflect different colors in a white light spotlight. Fox have close-set, amber colored eyes. Some cattle also have amber colored eyes that are set farther apart. Whitetail deer have greenish-blue eyes and some animals have reddish colored eyes.
With the red lense light, the width of the spread between the eyes is a good clue as to what predator has come to your call.
I'm new to this night time hunting as of this year, but have researched it extensively and have been successful in calling in, getting shots at, and harvesting some red fox.
I stopped deer hunting in mid-January and switched over to strictly night time predator hunting.
This is one of the greatest sports I have ever participated in, and I'm hooked and committed to becoming an experienced night time predator hunter.
Hope this helps.
JT