Electricity only looks blue because we usually see electrical energy as it passes through air. Electrons in each air atom gain energy from the electricity and jump to a more excited state. As the electrons return to their original energy level they release a photon of light. In air this photon appears blue but other gases would produce different colours. For example, the gases argon, phosphor, mercury and neon are used in this way to make the various colours in ‘neon’ lights.
Answered by Kate Mulcahy, Science Museum.