When alkali metals dissolve in liquid ammonia: $\text{Na} \to \text{Na}^+ + e^-$

The released electrons are trapped by cavities in the solvent and become ammoniated electrons ($e^-_\text{am}$). These solvated electrons absorb light in the visible range and are responsible for the characteristic deep blue colour of the solution.

At higher concentrations, the colour changes to bronze — indicating electron pairing.

Sodamide (NaNH$_2$) forms on prolonged standing or with catalysts, not immediately.