The rapid colour change in the rainbow lizard can be attributed to-

Comprehension:

The rainbow lizard is a common and conspicuous lizard. The mature male has an orange head and a brown, blue or black body. The middle section of the tail is also orange but ends in a black tip.The female is less brightly coloured; she has a brown head with green markings, a fawn body with brown patches down the back and yellow markings on the flanks, The male, about 30 cm long including 17 cm long tail, is longer than the female and often twice as heavy. Young males, not yet in possession of territory are indistinguishable by their colour from females. In both sexes rapid colour change, can take place, by redistribution of black pigment in special cells, the chromatophores, in the skin. When  the male is captured or handled or when he is fighting in defence of his territory, the orange colour in his head and tail turns to brown in 30 seconds and may revert to its original state after 3 to 4 minutes. The outer layer of the skin is shed two or three times a year.

At sunrise the lizards emerge from their roosting areas: they lie motionless on the vertical walls and bask in the sun. After 10-20 minutes of basking, the lizards move, one by one, down the wall and disappear into vegetation to catch insects, though they emerge from time to time and remain motionless in the sun. The intermittent basking is very important for their activities; the rate of chemical reaction in the body is increased with a rise in temperature, which enables muscle contraction, nervous conduction, enzyme secretion etc. to proceed more rapidly so that the lizard is more active in catching insects or escaping from predators. By basking, the lizard can raise its body temperature to about 38 degree centigrade, 10-18 degree above that of the surrounding air. Body temperature of above 40 degree is  liable to kill the lizard.