False colour processed image of the moon (increased saturation).
Although we think of the moon as being monochromatic, the irregular distribution of metals in the moon's basalt plains (seas) gives some variations in colour across the moon's surface. Sinus Medii (left, middle) is visible clearly as dark violet. Mare Tranquillitatis is similarly dark blue/purple. This shows higher concentrations of Titanium and Iron, making these basalt areas known as "metal rich basalts". The orange areas are highlands which are metal poor. As the basalt areas were formed by ancient volcanoes, I suppose their composition gives us some insight into what lies below the moon's surface (or did).