I recently conducted an oil painting class which focused on a night-time seascape theme. Rendering night scenes is always challenging, as colors diminish and things take on a more monochromatic feel. The issue is to get the scene dark enough to convey that particular time of the day, but not so dark that it literally becomes lost. In reality, some nights are pitch black and some are still quite light. It takes a lot of "judging" of the values to pull it off convincingly.
I find it easier to establish my mid-tone first and I use that value to "tone" my whole canvas. This sets the stage for the lights and darks I will apply which will straddle either side of that mid-tone.
Painting is all about value contrasts and I make sure that I still get a broad range. (Note the lightness of the moon and sea foam compared to the rocks.) However, the middle values are much "closer" together and vary only slightly. This is the key to capturing that night-time mood.
I have found that these "moonlit" themes seem to strike a certain chord with viewers and consequently, they are good sellers. By a large margin, most landscapes are portrayed during the daytime hours, so perhaps a moonscape's appeal lies in the fact that it's different. If you're strictly a "daytime" painter, don't be afraid to catch "full moon fever" and try one of these.
Just watch out for werewolves!