One of the mysteries of the English language finally explained.
1A greyish-blue colour.
2Angling. A small dark mayfly of the genus Baetis; an artificial fly made in imitation of it.
3Any of various blue pigments containing iron, especially. Prussian blue.
Of a greyish-blue colour; designating this colour.
Late 17th century; earliest use found in John Dryden (1631–1700), poet, playwright, and critic. From iron + blue.
iron blue/ˌʌɪən ˈbluː/
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