Anyone tried it?
I'm going to pick up some red clear lens cover tape and try it. Got some of those inexpensive LED flashlights which are pretty bright. Figured they may be a good addition for a rear light on pitch black winter months.

never tried it on a bike .. don't see any reason why it wouldn't work ... its going to diminish the brightness quite a bit though

crap, this brings back memories of my first tail-light - a plain old flashlight with the lens colored red by a magic marker.

You'll lose a lot of output relative to your battery life. In my experience LED tail-lights last far longer than LED headlights, and I consider this a major plus. If you take a "see" LED light and put a filter on it to turn it into a "be seen" taillight, you'll still only get only a few (single-digit) hours of use out of the batteries.

I don't see the point. There are plenty of red LED taillights that are plenty bright and very efficient. Why take a white LED (actually a blue LED and a yellow fluorescent material) and filter out most of its light with a red filter?

You will lose almost all the light output from said light. LEDs are not like incandescent or filament bulbs. A white LED puts out very little light on the red part of the spectrum. See my explanation here: https://www.bikeforums.net/showthread.php/775220-Those-wonderful-blinking-headlights!!!?p=13370643&viewfull=1#post13370643

You want a bright red light, use red LED emitters.

^ what they said. I put a red filter on a 145-lumen Fenix L2D, and its output dropped to about the level of my Planet Bike Superflash. I do own a cheap Ultrafire flashlight with a red emitter, which is quite a monster, but highly focused. It might be a good add-on light if you routinely ride in dense fog, although it doesn't have a flashing mode.

I Rit boiled the dome light in my old Mazda pickup way back when. Only downside is that doing the same to anything exposed to direct sunlight will fade for sure...in your case, possibly a nice shade of pink.

Seems unnecessary, even on a tight budget you should be able to find an inexpensive tail light that will hold a much longer battery life than any standard flash light. Also, I think the blinking function would make you far more recognizable as a cyclist.

Meh, I have the lights so figured I'd try but thinking of the wavelenghts of light it's probably not going to have much left after filtering. Didn't think about that.