I noticed the fading on the receipts as well . Several years ago, I started making photocopies of the receipts for my records so I can keep track. I do this at my office right after I buy something and they have not faded. I think it is a combination of the paper or ink used in the register receipts- it just doesn't last.
Since the photocopy of the receipt comes out in a letter size paper, I have used a hole punch and how have a very organized notebook with dividers for all my good things. Makes it really easy for insurance records too.