Solar modules absorb many different wavelengths of light. Light that is not absorbed is reflected. As humans perceive colours based on the light reflected by materials, the colour of a solar module is determined by its components. Most solar cells are made of polycrystalline silicon, which predominantly reflects blue light, making the cell appear blue to us. 🤓 However, you have surely also seen black solar modules before. These are made of monocrystalline silicon. ☀️
By the way: With today's technical possibilities, it is even possible to produce red, yellow, or green solar cells to make it easier to integrate them into the front of buildings, for example.