If I’m understanding what you are trying to say / what you are looking at?
I will try to explain, during manufacturing the lower half of the belt is molded, followed by the light colored (assuming Kevlar for that one due to the color) is then continuously wrapped around the lower portion of the belt (think level wind reel, one layer all the way across the mold, which may be many feet wide). Then they finish molding the upper / outer half. After curing the belts are removed from the mold, cut to width and appropriate angle. When it’s cut, you will see cord part of the way around and the rubber between the cords part of the way around. Very normal.
Like mentioned by the others, the rubber will glaze when it’s been slipping / getting overheated. This glaze has a much lower frictional coefficient and leads to even more slipping and loss of performance. (Similar to when your wife rides the brakes or clutch and fries the pads). lol
With proper clutching the belt should never slip, nor overheat. I have to laugh at the blow hole clutch fans, because if your clutching is actually working correctly the clutches and belt run pretty cool. You should be able to touch them without getting a burn, bare handed. FWIW
Sent from my iPhone using Tapatalk