You are going to need a lot more foliage and at least one or two real plants. It is hard to pinpoint what exactly is wrong when the care is not up to par. Can you fill out this form please? Some more pictures from different angles would be good as well.
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.
Jpf about the black marks. When chameleons are scratched or rub against things they may form black marks which I believe to be some sort of bruising of the skin. It is likely the chameleon rubbed it's nose against the mesh or even on a branch.
There are several things that don't seem right with your caging such as lighting and plants - which are essential. You should fill out the how to ask for help form above posted by Camryn. I think there may be some things we can point out to you that can make your chameleon keeping as trouble free as possible. These sort of things, if not corrected, can lead to the premature death of your chameleon. I hope you can find the time to fill it out, as soon as possible.