I notice an orange line on my 2006 Mazda 5 serpentine belt surface. Look like rust but not sure. The orange line looks so evenly distribute throughout on the belt surface I can wipe it off with my finger. It has 19,000 km. I bought it brand new and seldom drive it. I only seriously driving it last October when I sold my Honda. The belt looks fine no cracks. There is no belt squeak and noise and the AC works fine. There is orange dust in the belt tensioner pulley. The surface of the water pump pulley is half glazed. I guess it's from the contacting of the orange belt. AC belt looks clean. It had a regular maintenance an oil change and PCM reflash by the dealer couple months ago and they didn't say anything about it. Should I worry about it. Thanks for all your help!

 

Got some more pictures of the tensioner pulley and the water pump pulley. You can see the orange line reflects on the glaze part of the water pump pulley. (Should the surface of the water pump pulley not glazed at all?)

 

I would not worry about it.