Why is the flame of beryllium colourless?

The flame of beryllium is colorless because beryllium does not emit visible light when it is heated. Unlike other metallic elements that can produce characteristic flame colors due to electronic transitions, beryllium’s electronic structure does not allow for such transitions in the visible spectrum. Instead, any energy absorbed may result in excitation of electrons to higher energy states, but these transitions involve higher energy photons, which are outside the visible range. As a result, beryllium appears to burn without producing a colorful flame.