One method of calculating the chromaticity of the scene illuminant takes advantage of the fact that for heterogenous materials ( i.e. non-metals) the specularity, or surface (vs. body) reflection tends to directly indicate the illuminant chromaticity. Klinker, Shafer and Kanade [SKK85] model matte surfaces using a dichromatic reflection model, looking for characteristic clusters in a three-dimensional color histogram to characterize the illuminant. Lee [Lee86] uses a similar method with two dimensional histograms in the CIE color space to locate the illuminant.
While attractive due to the apparent simplicity of directly reading the illuminant from specularities, these methods require that specularity be present in an image. The human visual obviously requires no such cues, and experiments by Hurlbert [Hur89] indicate that specularity cues are often [wrongly] ignored by humans.