My only question is how in the devil did you use this bag for all that time and keep it pristine. Mine was a light buff colored buckskin, and now it looks like a grease rag, with powder stains, patch lube stains, and blood stains,and those are just the stains I can identify. You can darken the bag using some of the processes mentioned, or you can darken it by using any type of oil used to weatherproof shoes and boots. You can lighten it by soaking it in Rit dye remover, and then drying it in the sun, and then re-breaking it in the dryer, on air only, with some tennis shoes thrown in to do the breaking.
Hungry Horse