Why are halogens coloured ?

Explanation

Halogens absorb light in the visible region, which result in the excitation of outer electrons. Fluorine having small atomic size absorb higher energy violet radiations and the transmitted light appears pale yellow. On the other hand, iodine with large atomic size absorb lower energy yellow and green radiations and thus transmitted light appears violet.
Colours of Halogens :
Fluorine`" "`Chlorine`" "`Bromine`" "`Iodine
Yellow`" "`Greenish Yellow`" "`Orange red`" "`Violet