What are the temperatures in your tank? I'd swap out the flukers bulb with a ZooMed Repti Basking Spot light because the flukers (I believe) use a neodymium coating which filter some colors to make them look better to us but can cause distortion with your dragon's vision. I'd replace it with an equivalent wattage if your temps are on or adjust accordingly. You want the basking site to be about 100-110 and the cool side of the tank to be about 75-80 during the day.
Is the ReptiSun 10.0 you're using a tube or a coil? If it's the tube, you'll want to make sure it's mounted about 6-8'' right above the basking spot for optimal output.
The discoloration on his head looks like the area is getting ready to shed to me so that's good. Proper heat and lighting will likely help his appetite come back.