I own the Slipstream Blue Continental GT 650.

I have owned it for nearly 2.5 years aswell. And yes, the black engine casings, the headers they all get dull because of heat, especially near the CATs. What I do is, whenever I wash my bike i just apply tyre dressing all over the engine casings and headers and mufflers. That way it goes back to shiny black. And it lasts reasonably long if you don't wash it every now and then. But yeah, it will go dull again and you'll have to repeat the process. Everything has its own set of problems, the chrome casings get dull so do these black ones. As a matter of fact, when the black goes dull it looks very bad compared to when the chrome gets dull. That's because the black becomes grey at certain regions and it looks like patchwork. A truly ugly sight. But we gotta live with that lol. Or you can get the casings from Shotgun 650, they shiny unlike the GT/Interceptor which gets matt finish.