They start showing color changes when they are about 3-4 months old. It is not a drastic change and is mostly based on emotion levels and heat. If they stay darker they are absorbing heat. If they puff up and show spots and more dominant patterns then it is a back off warning.
If you want us to check your husbandry then please fill out this form and post pics of your entire enclosure lights down. Chameleon Info:
Your Chameleon - The species, sex, and age of your chameleon. How long has it been in your care?
Handling - How often do you handle your chameleon?
Feeding - What are you feeding your cham? What amount? What is the schedule? How are you gut-loading your feeders?
Supplements - What brand and type of calcium and vitamin products are you dusting your feeders with and what is the schedule?
Watering - What kind of watering technique do you use? How often and how long to you mist? Do you see your chameleon drinking?
Fecal Description - Briefly note colors and consistency from recent droppings. Has this chameleon ever been tested for parasites?
History - Any previous information about your cham that might be useful to others when trying to help you.
Cage Type - Describe your cage (Glass, Screen, Combo?) What are the dimensions?
Lighting - What brand, model, and types of lighting are you using? What is your daily lighting schedule?
Temperature - What temp range have you created (cage floor to basking spot)? Lowest overnight temp? How do you measure these temps?
Humidity - What are your humidity levels? How are you creating and maintaining these levels? What do you use to measure humidity?
Plants - Are you using live plants? If so, what kind?
Placement - Where is your cage located? Is it near any fans, air vents, or high traffic areas? At what height is the top of the cage relative to your room floor?
Location - Where are you geographically located?
Current Problem - The current problem you are concerned about.
The more details you provide the better and more accurate help you will receive.