AIEEE 2002 Chemistry Solved Paper

The alkali metals dissolve in liquid ammonia without evolution of hydrogen. The metal lose electrons and combine with ammonia molecule.
M→M+(in liquid ammonia) +E−(ammoniated) M+(x+y)NH3 →[M(NH3)x]++

e−(NH3)y

Solvated electron

It is ammoniated electron which is responsible for color.