Thanks team, some good answers. On most occasions it is suggested that a Chameleon changes colour for defensive purposes. It seems that they can do this by changing the tension in their skin. Not something that we can do very easily. For the Chameleon, part of the skin is a compound that can be stretched and it is this compound that changes the light colours that are absorbed by the skin and those that are reflected. Thus the colour change.
Reflection of light of things depends on the material and the light that is falling on it. Suppose green light was shone on a red object in a dark room. Would you see it? Sometimes you can also notice that changing the temperature of a material changes the way it reflects light. Running a hot iron over a red material changes the ‘redness’ of the material because of the effect of the heat on the compound that the red dye is made of. Some experiments that you might try (with the help of an adult).