I had a recent post involving the same concern. Not as much
yellow as yours, but I thought it might be due to temperature.
If your room is too cool, then the humidity may not build up enough,
and the temp in the tank cools down. I put some plastic over my tank
setup and created a tent, so the warmth of the lighting will increase
the temp. under the tent. I don't know if this is the answer but I
thought I would try it.