Organismal characteristics of ectotherms are profoundly affected by body temperature (Tb). Despite constraints imposed by environmental factors, they can adjust Tb by several means. However, if thermoregulatory ability is limited by their own property such as coloration and this constraint affects individual's fitness, selection may promote coevolution of coloration and thermal aspects. I investigated this topic using a colour-dimorphic (melanistic/striped) snake Elaphe quadrivirgata as a model species. Recent laboratory experiment revealed slower body warming in striped individuals than in melanistic individuals. Under this circumstance, one way that striped individuals can manage their slower body warming is to prefer low Tb. Contrary to this prediction, there was no intermorph difference in preferred Tb. Coupled with the results of field studies, I suggest that striped individuals manage their slower body warming by behavioural thermoregulation and that constraints (e.g., high predation risk due to conspicuousness under thermally superior habitats) imposed on melanistic individuals lessen their thermal advantages. The effect of melanism on thermal aspects may not be so advantageous for melanistic animals than generally thought.