The Master thesis deals with the colour stability of three surface modifications applied on the thermally modified and unmodified maple, birch, beech and alder wood. In the case of maple, birch and alder wood, two modes of thermal modification with the temperature of 105 °C and 135 °C were applied and in the case of beech wood, it was also modified with the temperature of 125°. Three types of surface modifications were applied on the modified as well as unmodified wood (based on synthetic, wax-oil, and water). The colour of the wood and thermo wood surface was measured using the CIE Lab colour space prior to coatings and after the surface modification in exactly determined points. The effect of the type of transparent surface modification on the colour change was investigated. Consequently, the samples with modified surfaces were exposed to solar radiation behind the window in the interior for 60 days. The colour of the surface was measured at the exact time. The results showed that the wood colour after application of the coatings on all surfaces changed. The surface colour varies and the differences can be seen by naked eye. The significant change in the surface colour due to the solar radiation in interior was observed in the case of all surface modifications during the first 30 days. The colour change in individual tree species was different and depended on tree species, thermal modification and especially on the type of surface modification.