Argo, please excuse this slightly off Topic post, but your title caught my attention and I figured perhaps it was something related enough to be of some interest.
I experimented with this principle of corralling off-angle/side-angle light to a different situation - green tint-shift.
I observed that a fair amount of tint-shift results from stray light from the sides of prone emitters. In my experiments, I placed “Magenta Collars” around the perimeter of emitters in an effort to filter out green, with some success.
Some of my earlier experiments that were successful, ultimately failed but did put me on my current track.
Here is an example of what I earlier called a “Magenta Collar” attached around the cavity of a LED spacer -
It would be placed inside a light such as this -
Notice the tint affecting primarily the side off-angle which appears at center of the reflector -
And here are the results of original beam (on left) and beam after a Magenta Collar (on right)-
The same light, with the same emitter, taken at the same exposure and white balance, with the only difference being the Magenta Collar! The green is reduced without dramatically tinting the rest of the beam as a lens tint filter might.
I mentioned that my experiment with the Magenta Collar failed, that was primarily because the plastic melted from the high heat of the LED. I suppose a collar made of higher heat capable material could be done but I’ll leave that for others to pursue.
It was my latest approarch, similar to your post (and as it turns out djozz’s) of a directly painted/tinted collar where I’ve settled for now. Here for example is an XP-G3 (notorious for green tint-shift) where I magenta tinted directly on the base/bottom perimeter edge of the led itself. It was equally as effective in reducing green tint-shift in the beam. This approach was also less construction dependent. (Sorry no before/after photos for comparison as removing the tint from the emitter dome is more involved than simply removing a physical Magenta Collar from a spacer.)
This magenta collar approach could be something for fellow tint-snob to consider to help with (but unfortunately not entirely eliminating) green tint-shift. It has the added benfit of less light loss than lens filters.
In any event, I’m putting this out there for consideration. Perhaps someone can make Magenta Collars available commercially.
(3D printer anyone? Or BanL/BG interested?)