Dreadnought dio painting

I've had a long session with the airbrush last night, and started reworking the lights on the dreadnought diorama.I picked up some burnt sienna ink for the torches, to replace the burnt umber I used before. I think this contrasts nicely with the blue overhead lights.(the burnt umber was too yellowish).

The only problem I have now is that in real life the blue sky light is way too saturated (doesn't look like it in the photo), so I need to desaturate this on the model...Any ideas how to go about this without the obvious "repaint it all" method?I'm thinking glazing over with some grey, but I'm not sure...