The gauge lighting is very strange. During the twilight period only the "spotlights" come on but the gauges stay dark, which looks very, very odd. Only when it's getting really dark outside do the gauges actually change to their lit counterparts. I think they should change to the lit status as soon as the spotlighs come on:

Yeah I think it's an FSX lighting bug - my Citation X has that too. It's the few minutes between dusk and night where the gauges are very hard to read and very dark.