So, is there anything we can learn from staring at that graph? The first thing to notice is that the graph slopes. It rises almost monotonically from the shortest wavelengths to the longest wavelengths. This is known as a "red" spectrum -- it's brighter in longer, redder wavelengths than in shorter, bluer wavelengths. A spectrum that sloped in the opposite direction would be thought of as "blue," and a spectrum that was pretty flat across all wavelengths would be described as "gray." (The Moon is a good example of a place that's spectrally gray.) So Mercury is "red." Reddish colors on rocky surfaces in the solar system generally indicate places that have been exposed to space weathering for some time. Fresher surfaces, like the interiors and ejecta blankets of fresh craters, tend to look gray or blue by comparison to the reddish surfaces they've punched in to. Just take another look at that global shot of Mercury above -- you can see a couple of fresh crater splashes on the surface, and they look blue.