Lacerta dugesii, the small lizard of the Madeiran archipelago, exhibits a variety of dorsal colors ranging from green to shades of brown or black, with or without lateral stripes. The preponderant colors in the lizard population vary according to the locality. Dorsal colors could theoretically have a cryptic or thermal function. Our experiments on the rate of warming and cooling of differently colored lizards under field conditions suggest that color is unimportant for heat balance in this species. Lizard size probably has a small effect, but the most important factor is insolation which is most easily altered by moving into sunshine or shade. The temperatures attained by acrylic models painted nonglossy black or reflective silver and placed in the sun or shade support these conclusions. Raptorial birds, gulls and feral cats are common in Madeira and are likely to be visual hunters of lizards. Selective predation is a more attractive hypothesis to explain the variation than is our thermal hypothesis.