Mercury is typically white, but its low altitude (angular height over the horizon) causes it to take on a pinkish tinge, similar to how the sun appears reddish at sunrise or sunset (indeed, both Venus and Jupiter can appear orange-red when they are close to the horizon). White light contains all colors of the spectrum, so mercury looks black because it's absorbing all wavelengths of light.
In fact, if you looked at mercury right now it would look black because it has an albedo (reflectivity) of 0.5-0.7. That means that it is reflecting half of the incident light and absorbing the other half.
Albedo varies by wavelength. Blackbody radiation has an intrinsic temperature of about 3000 K, so it has a characteristic color which depends on its emission spectrum. At infrared wavelengths where Mercury's atmosphere is transparent, albedo is high (about 0.9) because it's made of silicate rock. At visible wavelengths where the atmosphere is not transparent, albedo drops down to about 0.3 because it's dark gray colored carbon dioxide with some greenish patches from oxygen in the air.
The color of mercury has nothing to do with its being covered by Earth's atmosphere. It is always white from space because darkness is defined as complete absence of light, not absence of everything else besides light.
Mercury's sky would be black during the day, not blue, since the planet has almost no atmosphere to disperse the sun's light. However, because of its proximity to the Sun, some of that light does make it through the solar system's second-closest planet before reaching Earth, so at night the sky would be bright enough to see from Earth. Its daytime color would be dark gray or black.
Earth's moon will always be visible in the night sky, even when the Sun is out. Because Mercury has no appreciable magnetosphere to protect it from charged particles streaming from the Sun, every hour or so it gets a global blackout as electrons from the Sun flood into its upper atmosphere. During these times, the only things visible in the night sky are its four small moons: Marcy, Miller, McCubbin, and Webster.
In addition to these satellites, observers on Earth can see stars move across the sky when Mercury is rising or setting. These stars are not actually moving relative to each other, but rather they're all moving together in straight lines away from or toward the Sun.
Planets' colors are determined by what they are made of and how their surfaces or atmospheres reflect and absorb sunlight. Mercury's surface is dark gray and stony, with a heavy coating of dust covering it. The surface is believed to be composed of igneous silicate rocks and dust. Beneath the crust is a dense mantle of rock and metal.
In contrast, Venus is white because its cloud-covered surface reflects much of the sunlight that reaches it. Some scientists believe that a deep layer of water may cover part of Venus' surface. This would explain why the planet is warm enough for life as we know it.
Mars is red because there is evidence that water once flowed on its surface. There are still canals in Mars' southern hemisphere that were most likely made by water. In addition, studies using NASA's Curiosity rover have found strong evidence that ancient conditions on Mars could have supported microbial life.
Jupiter is blue because it is made up of clouds and gases. Its atmosphere has hydrogen molecules, helium, and ammonia (which makes it less dense than air and so floats above the planet's surface).
Saturn is yellow-orange because it is covered by a thin veneer of gas and particles that was blown off of Jupiter over millions of years. Inside Saturn is a large moon called Titan that has a thick atmosphere rich in methane.
The major lines in mercury have wavelengths of purple (405 nm), blue (436 nm), blue-green (492 nm), greenish yellow (546 nm), yellow (577 nm), orange (623 nm), and red (691 nm). Keep in mind that 1 nm equals 10-9 m. Therefore, 1 cm is 10-3 m and 1 mm is 10-6 m.
These colors are due to light waves with different lengths when they reach the surface of the mercury droplet. If you look at a rainbow, you can see all the colors of the spectrum within each drop of water. The same thing happens with mercury: it forms drops of liquid with different sizes which reflect light of different wavelengths back into the sky.
The size of the droplets depends on how far away the mercury is from the heat source. If the flame is very small, then the droplets will be large. As the flame gets bigger, so too will the droplets become smaller.
This phenomenon has many applications. For example, it can be used to create lights of various colors for decoration or entertainment. Or, more importantly, for science! The properties of mercury can then be used to study other elements using spectroscopy.
Spectroscopy is the analysis of the composition of matter by studying the effects of such substances as radiation, electricity, or temperature upon them.