Editing Blue (section)

==Shades and variations==
{{Main|Shades of blue}}
[[File:Color icon blue.png|thumb|Various [[shades of blue]]]]
Blue is the colour of light between [[Violet (color)|violet]] and [[cyan]] on the [[visible spectrum]]. Hues of blue include indigo and [[ultramarine]], closer to violet; pure blue, without any mixture of other colours; Azure, which is a lighter shade of blue, similar to the colour of the sky; Cyan, which is midway in the spectrum between blue and [[green]], and the other blue-greens such as [[Turquoise (color)|turquoise]], [[teal]], and [[aquamarine (color)|aquamarine]].

Blue also varies in shade or tint; darker shades of blue contain black or grey, while lighter tints contain white. Darker shades of blue include ultramarine, [[cobalt blue]], [[navy blue]], and [[Prussian blue]]; while lighter tints include [[sky blue]], [[azure (color)|azure]], and [[Egyptian blue]] (for a more complete list see the [[List of colors|List of colours]]).

===As a structural colour===
{{Further|Structural colouration}}

In nature, many blue phenomena arise from [[structural colouration]], the result of interference between reflections from two or more surfaces of [[thin films]], combined with refraction as light enters and exits such films. The geometry then determines that at certain angles, the light reflected from both surfaces interferes constructively, while at other angles, the light interferes destructively. Diverse colours therefore appear despite the absence of colourants.<ref name="ExeterIridescence">{{Cite web |date=September 1998 |title=Iridescence in Lepidoptera |url=http://emps.exeter.ac.uk/physics-astronomy/research/emag/themes/natural-photonics/iridescenceinlepidoptera/  |archive-url=https://web.archive.org/web/20140407082122/http://emps.exeter.ac.uk/physics-astronomy/research/emag/themes/natural-photonics/iridescenceinlepidoptera/ |archive-date=7 April 2014 |access-date=27 April 2012 |website=Natural Photonics (originally in Physics Review Magazine) |publisher=University of Exeter}}</ref>