Cesium why blue in alkali?

Answer 1

Caesium metal is gives a bright blue solution when dissolved in liquid ammonia. The dissolving is believed to cause the production of caesium ions and a free electron. a similar blue colr is produced by sodium, potassium and rubidium.

In aqueous alkali solutions caesium ion is colorless and therefore unless the anion is colored the solution is colorless.

Answer 2

Cesium and other alkali metals appear blue in flame tests because of the specific energies of the electrons in their atoms. When heated in a flame, the electrons in cesium jump to higher energy levels, absorbing energy and then emitting it as light in the blue part of the spectrum. This characteristic blue color is unique to cesium and distinguishes it in flame tests.