I'm stupid and don't remember the color of the "books", but the digital CD-R format is piggy-backed on top of the analog CD format. (for what that's worth)
A fellow down the corridor from me had a job investigating the archival quality of write-once and RW CD and DVD disks. As far as I know, he just use elevated temperature to speed aging. He could control humidity, so that may have been involved as well. Bright light is KNOWN to cause more-rapid aging.
The raw error rate of CDs is vaguely one error in a million bits - far too bad to be useful. Various redundancies and error correction are built into the recording standards.
As disks age, they have more and more errors until the number and location of errors becomes too great for the error correction to handle. One needs to transfer the data onto another disk before that happens. Note that you want to copy the __files__ while error correction can still fix the errors. Sector-by-sector, track-by-track disk duplication will just transfer the errors to the new disk! BAD!!
Some CD and DVD drives and their reading software can report how hard the error correction is working to repair the errors on the disk being read. Keeping track of this information gives a better measure of how each of your disks is degrading over time. Unfortunately I don't know which drives and software have this feature - though the fellow gave me a Plexstor software disk. I haven't tried it.