However, it is the color displayed on http://www.international-klein-blue.com/, so I guess the Web rendition of IKB is #002FA7. This is very far from the color specified by French artist Yves Klein (28 April 1928 - 6 June 1962). I once was in a room full of his paintings at the Kunsthaus in Zürich, and the effect was stunning. One trick was that these painting are correctly displayed by hanging them projecting out slightly from the wall, so that the canvasses appear to be suspended in space.
The ultramarine IKB paint is applied on the canvas with thick, highly textured strokes. Take the time to sit on a bench in front of a solid IKB painting, and the painting will hit you. The chromaticness is as high as it can get, and the few S-cones in your retina are contribuing to your visual system as they never have before. It will teach you, what the "deep" in "deep blue" means.
Klein started using IKB in 1958 and between 1960 and 1961 he created 15 monochrome IKB paintings. He developed IKB with chemists to achieve paint with the same chroma as dry pigment. This is done by suspending the pigment in a clear resin, and it allowed him to obtain the first patent (actually, just an enveloppe Soleau) for a color. As far as I know, IKB was never produced commercially.
Speaking of commerce, there is an interesting story about the first exhibition at the galleria Apollinaire in Milano. The eleven canvasses, although identical, were not appreciated equally by the public — they were sold for different prices. Klein concluded that each painting, as well as its material reality, was impregnated with an immaterial quality that made it distinct from the others.
And now I already see Nathan planning his next post, where he will not ask you to name colors, but to price them…