When you take a torch to a material like wood and burn it, it turns black and peels like a dry lake bed. If you don't go so far as to turn it to a black charred surface, you have a bit of a spectrum of color change. It darkens, turns brown, and then eventually turns black. It turns black because it's reflecting less light (or absorbing more). The same way a sound damping material absorbs certain wavelengths of air pressure movement, which we refer to as sound.
This is essentially what is happening to the chrome surface of the exhaust pipe, but at a microscopic level. It doesn't "dye" the surface, as much as it creates microscopic canyons and texture that traps longer wavelengths of light, which allows shorter wavelengths to bounce off. Longer wavelengths of light are more red, shorter and more blue (redshift / blueshift). The gold color is pre-blue, it'll eventually turn blue. It's a sign that hot air is bombarding the "kink" in the exhaust pipe as seen below, which causes more friction, slows down because the particles have to wait for the faster moving particles next to it, and as we all know, friction causes heat.
This is essentially how anodizing titanium works with electricity (aluminum anodizing is actually a dye). You're corroding the surface with electrolyte and a charge to create microscopic texture that traps certain wavelengths of light, filtering them out, and allowing other wavelengths to bounce off and be detected the electromagnetic sensing components in your cranium (your eyeballs).
Light and color doesn't actually exist, your eyes detect certain frequencies of electromagnetic energy waves and particles and your brain converts these pulses and frequencies into color and "brightness".
You can remove the color by polishing the surface and smoothing it out so it reflects a more consistent wavelength of electromagnetic energy (light).