A Pale Pink Dot
Unless you are in the tropics (or witness a total solar eclipse), you will never see Mercury in a completely dark sky, because when the Sun far enough below the horizon for the sky to be dark, Mercury will be below the horizon too. You have to be in the right place at the right time to see it at all. Discounting total solar eclipses, which are extremely rare, the right place is anywhere with a clear, low horizon in the direction of either the sunset or the sunrise as appropriate. The right time is after sunset as the sky darkens, or, for early risers, before dawn. Even that will do you no good unless you have also chosen a date to coincide with Mercury’s brief excursions far enough from the Sun for it to be sufficiently high above the horizon for it show itself in the brief interlude between daylight and full darkness. I have often glanced unawares at the sky and seen Venus shining high and bright in the evening or morning sky. You can hardly miss Venus when it’s around, but I’ve never seen Mercury without deliberately setting out to look for it.