From Wikipedia:
"In terms of the visible spectrum, "brown" refers to high wavelength (low frequency) hues, yellow, orange, or red, in combination with low luminance or saturation"
http://en.wikipedia.org/wiki/Brown
(And what on Earth does Wikipedia mean by a ''high wavelength''? In over 40 years of working in radio, I've never heard of wavelength being so described.. Frequencies are higher or lower, yes, but wavelengths aren't - they're longer or shorter.)