Stained glass won’t (I think) shift any frequencies. It will attenuate different frequencies differently, but it won’t make up new ones.
So when the signal frequency changes, you’ll still see that change, but the light might get brighter or dimmer at the same time due to the stained glass. But you don’t care about the brightness to begin with.
So when the signal frequency changes, you’ll still see that change, but the light might get brighter or dimmer at the same time due to the stained glass. But you don’t care about the brightness to begin with.