Hi Lurker,
TRADE SECRET! Go buy the cheapest satin black aerosol you can find. Pop the repeaters out, and spray them. Unless you give them seven heavy coats, the light intensity will NOT be affected.
My preference is to "waft" a couple of light coats on, so the original colour is ...Almost detectable..... but even with a solid coat, the light level WILL be OK.
Two best bits;
First, it is -essentially- free.
Second, If you dont like it, a quick wipe of thinners, or a moment with T-cut will take it back off with no ill effects, (unless you gave it seven heavy coats......)
Bad bits;
You may need to re-do it every couple of years. Unlike the e-bay copies, the E-marks are intact.
It works equally well on tail-lights and front indicators; For rears, I tend to leave reverse lights and Fogs un-tinted; it gives a "factory" look.
PLEASE don't spend a week on the forum discussing this; try it!
It works better than you will believe.
ScotAlan