I have been looking at photographs of the planet Mercury, and I notices that in most of the pictures I have seen, the rocks on the surface seem to be covered in blue in green. From this, is it correct to say that the surface of Mercury is mostly made up of copper deposits?
I think you probably fell into a trap concerning color-coding.
In reality, mercury is dark grey and mostly covered in silicate rocks/dust.
From a scientific point of view, the "real color" of an object like mercury is of little interest. What's more interesting, is it topography etc. To make it easier to interpret data, man often uses color-coding (since our color-vision is quite ok) to communicate different information about such things.
Or ist just about beauty: When you see pictures of nebulae like the pillars of creation you notice they are in a lot of different colors. This is because a lot of the radiation is not in the visible spectrum, and you can "color-code" it to make it interesting to look at.