[Shiraz (Ray)]

I doubt that anything is wrong. The QHY8 is most sensitive in green and the LED source may have a lot of green as well.

Its a while since I used flats (IRIS or StarTools can get rid of uneven backgrounds), but I think that the Nebulosity manual recommended using flats before deBayer.

If you apply a greenish flat (deBayered or not), it will bias the light frames to have reduced green, but you can correct for that easily enough - might even get rid of some skyglow. suggest that you use the greenish flat and see what it does.

edit: just found a flat I once took with my QHY5 OSC with sunlight as the source - looks similar