yes they colours vary by locale (area of madagascar they come from) by 'morph' by sex and by mood.
you can tell what locale a panther is by looking at the colours. for example a nosy be (the most common locale) is completely different from say an ankaramy. a nosy be being mostly blue with red and yellow colour range and an ankaramy being pink with blue. they are both panther chameleons but as different as chalk and cheese.
have a look here to get an idea
they also vary within locales to a degree. so a nosy be can have slightly different colours i.e red or yellow eyes or more blue and less red on the body by individual yet the colour pattern tends to remain indentifiable to 'nosy be'.
they vary again by sex. the males exhibit the colours where most females are varying shades of pink (once again dependent on locale). also there is a change in colours with gravid females.
and once again by mood. as welshgaz has already said they will change their colours depending on mood and the satisfaction with their environment. this is a 'language' that once understood will enable you to understand your cham and give it what it needs. is the same for most chameleons...even those with limited colour changing abilities.