Just read the sad story of a guy who commented the outcome of his attempt to retrobright.
His conclusion was:

assasincz wrote:

... I wish it did not happen.

This makes me wonder again why all this retrobrighting.

The simplest way to reduce the stained look is to change illumination.

The "modern" illumination (FL, HID, LED) has no contiguous spectrum.
To achieve "warm" lighting (<3300K), there are added some strong peaks in the red spectrum.
This can result in brownish colors looking really ugly.

In my workshop (3000K) my Mac keyboard looks like an Urodore 64.
In my computer room (4200K illumination) its color appearance is sweet like an Apple II.

So I'd like to make you aware that changing illumination in your retro room to neutral (4000K-5000K) or "cold" (6000+K)
might be an easy alternative to retrobrighting for getting more acceptable colors.