The colour of the sky on a clear day and of deep water.

Adjective. Used before nouns: 'a blue sky', or after verbs: 'the sky is blue'. Common collocations: blue eyes, sky blue, navy blue, blue jeans, out of the blue (meaning unexpected).

Blue is one of the most popular colours in the world and is often associated with trust, calm, and sadness. In English, feeling 'blue' means feeling sad. 'Blueprint' originally referred to a type of technical drawing.