A total of six washed French and Algerian kaolins were studied. Kaolinite, halloysite, muscovite, feld-spars, anatase, rutile, gibbsite, goethite, and todorokite were present. The thermal behavior of the samples was studied and the transformation heats were determined and quantified by differential thermal analysis. Calcined samples from 900 degrees C to 1400 degrees C are studied by X-ray diffraction, the results show that the crystallite sizes of mullite rises as the temperature rises. The calcined samples showed an inverse correlation of L* and the crystallite sizes of mullite due to the incorporation of chromophore elements (Fe3+, Ti4+ and Mn2+) in its structure. Muscovite and rutile phases decreased lightness and increased chromaticity. The reduction state of Fe3+/Fe2+ and Mn4+/Mn2+ at 1400 degrees C enhanced lightness leading to the diminution of the b* parameter. The CIELAB color parameters were significantly affected with mineralogy and chemical compositions of the samples. Lightness of the natural kaolins is decreased (L* < 59) when organic matters beside manganese and iron oxides are present. L* was not affected when only iron (Fe2+) is present in the kaolin; however, the chromaticity is increased (b* > 22). Whiteness and tint indices (W-10, T-w,T-10) revealed that only one kaolin could be considered white (limits of CIE Colorimetry, 1986), though upon calcination, this number is enhanced to two. (C) 2013 Wiley Periodicals, Inc.