Hi Barkest,
Thank you so much for your advice. I have followed it and sure enough the walls look fine when they are on their own. I then eliminated everything else to discover it is definitely electrical devices-lighting that's causing the problem. So how can I adjust or completely turn off the illumination coming from the lights so that I still have the fitting in the picture, but it's not bleaching the walls! Some of the lights have a light brightness scale in the object info palette. But some of the lights I've put in don't seem to have that. I have played around with the ones that have this and I managed to make it look a bit better by having them all on 100% brightness (see attached image), but there is still a real difference between the two walls. I tried putting them all at 0 and it just looked like it did before. Is there a way to control the other lights? Or an overall way to control this? I need the lights but I'd also like the walls to not be black!
Thank you so much for your help.