Maybe this helps someone:
I've been using Aurora EL-foil (by Gerd Neumann) to take flats with my unmodded EOS 600D. Fine. R:G:B is 0.7 : 0.98 : 1 (some bluish white).
Then I used it with the same camera and the Baader UHC-S booster filter. R:G:B is 0.06 : 0.83 : 1 (medium blue). The low level of red introduces some noise to the flats that I fought down by taking 100 flats.
Now I ordered cheap color foil for stage/disco spotlights and tried different colors. My goal was to tame blue and green but not too much, so that I can still use it without the filter. Furthermore I want to use it with a 7nm Ha. It turned out yellow an pink are both well suited:
yellow with UHC-S: 0.81 : 1 : 0.95
yellow without: 0.85 : 1 : 0.74
pink with UHC-S: 0.88 : 0.93 : 1
pink without: 0:76 : 0:76 : 1
Both have the same intensity at Ha. I took yellow for the camera measures exposure with an emphasis on green. To avoid an over exposure I want green to be the strongest.
Of course the values differ for different cameras and for different filters. But if you find one channel far too weak the foil is a way to go. I put it inside the aurora (as one does with the NDs), so same handling as before.
(Values have been measured from raw without white balance in PI)