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Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy...

Blue is a colour, the perception of which is evoked by light having a spectrum dominated by energy with a wavelength of roughly 440–490 nm. It is considered one of the additive primary colours. On the HSV Colour Wheel, the complement of blue is yellow; that is, a colour corresponding to an equal mixture of red and green light. On a colour wheel based on traditional colour theory (RYB), the complementary colour to blue is considered to be orange (based on the Munsell colour wheel). The English language commonly uses "blue" to refer to any colour from navy blue to cyan. The word itself is derived from the Old French word bleu. The modern English word blue comes from the Middle English, bleu or blwe, which came from an Old French word bleu of Germanic origin (Frankish or possibly Old High German blao, "shining"). Bleu replaced Old English blaw. The root of these variations was the Proto-Germanic blæwaz, which was also the root of the Old Norse word bla and the modern Icelandic blár, and the Scandinavian word blå, but it can refer to other non blue colours. A Scots and Scottish English word for "blue-grey" is blae, from the Middle English bla ("dark blue", from the Old English blæd).