Prism

A medium that distorts, slants, or colors whatever is viewed through it.  *dictionary entry

In optics, a piece of translucent glass or crystal used to form a spectrum of light separated according to colors. Its cross section is usually triangular. The light becomes separated because different wavelengths or frequencies are refracted (bent) by different amounts as they enter the prism obliquely and again as they leave it. The shorter wavelengths, toward the blue or violet end of the spectrum, are refracted by the greatest amount; the longer wavelengths, toward the red end, are refracted the least. From: Infoplease.com

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