My main workspace faces north-ish and in winter the light is this flat grey thing that flattens everything I'm cutting. I know people who chase the sun around their house with their work, move their table every few hours. I just... work in it. Put a task lamp on it and get on with it. The colours look different when the piece finally gets into proper light anyway, I've learned to allow for it. My conservation teacher used to say you should only ever judge a mosaic in the light it's going to live in, which is fine if you're doing a floor for a church in Palaiokastritsa, not so helpful when your client's living room faces west and you're working under a cloud.