When an alkali metal dissolves in liquid ammonia,the solution can acquire different colours. Explain the reasons for this type of colour change.

(N/A) When an alkali metal is dissolved in liquid ammonia,it results in the formation of a deep blue coloured solution.
$M + (x+y) NH_3 \longrightarrow M^{+}(NH_3)_x + e^{-}(NH_3)_y$
The ammoniated electrons absorb energy corresponding to the 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.