Said belt is wide ( 8 1/2 inches in width) dark and shiny, without obvious scratches or marks of any kind and with 1/2 inch strip, light colored on left side when door is opened. Belt is not colored and appears shiny black. It has obviously been marked with toner either blue or cyano in the stripe described. Replacing said belt would be a major repair in my estimation. I'm not sure that you're seeing the inside door of this HP Laserjet 2600n printer?
My disappointment is that you don't apparently have my particular printer in mind and are answering in a generic sense. My HP Laserjet 2600n has but one belt. About 8 1/2 inches wide. Black and shiny. I fail to see how daylight will effect the stripe which appears to be diminishing in intensity with use. I will replace the cyano cartridge and the others also. I'll also wipe the belt lightly with a clean, lint free piece of paper towel.