Colour evolution and colour changes were analyzed from small specimens of three heat treated wood species using the CIE L*a*b* colour space. Upon heat exposure, the wood substance became darker of species; this was accompanied by a steady reduction in lightness. As treatment conditions (e.g., time and temperature) increase, various shades of yellow were favoured for the surface of red-bud maple wood (Delta b = 1.22-9.79). For European hophornbeam wood, increased times at elevated temperatures make a blue (-b) colour the better choice. The total colour difference (Delta E) of the surfaces of wood substrates appear to be well correlated with the treatment temperature and time. The FTIR spectra suggest that the level of modification was insufficient for removing the major cell wall constituents of the wood substrates. All heat-treated samples showed much less stability against colour difference in outdoor conditions. For red-bud maple, the greatest improvement was achieved for samples that were treated at 150 degrees C for 2 h (Delta E = 3.12). However, heat-treated oak wood had much less stability of colour difference for treatment conditions of 150 degrees C for 10 h. (C) 2010 Wiley Periodicals, Inc. Col Res Appl, 36, 462-466, 2011; Published online 7 October 2010 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/col.20634