Why are halogens coloured?
Halogens are coloured because of their low ionisation energy.
As a result, the electrons get excited in the visible region of light.
The remaining light falls in the visible region and halogens appear to be coloured.
For example: Fluorine absorbs wavelengths corresponding to violet light and the remaining light appears to be yellow. Thus, fluorine has a yellow colour. Similarly, chlorine is greenish yellow, bromine reddish and iodine is a violet solid.