When an alkali metal dissolves in liquid ammonia the solution can acquire different colours.

When an alkali metal is dissolved in liquid ammonia, it results in the formation of a deep blue coloured solution.

$\mathrm{M}+(x+y) \mathrm{NH}_{3} \longrightarrow \mathrm{M}^{+}\left(\mathrm{NH}_{3}\right)_{x}+\mathrm{e}^{-1}\left(\mathrm{NH}_{3}\right)_{y}$

The ammoniated electrons absorb energy corresponding to red region of visible light. Therefore, the transmitted light is blue in colour.

At a higher concentration (3 M), clusters of metal ions are formed. This causes the solution to attain a copper–bronze colour and a characteristic metallic lustre.