Yeah, you can read the ATIP Absolute Time in Pregroove - Wikipedia with any CD-R compatible drive. Writable media must have this info, or else the laser can’t track the groove of a “blank” disc, or set the writing power of the laser.
On Linux, and Solaris or where ever you’ve installed Schily’s CDR tools, you can read this info with just “cdrecord -atip”. OS X you can use “drutil atip” (or Finder and Disk Utility will also say something about it, I think). There’s probably something in Windows, but I haven’t done the research.
Also, sometimes there’s a human readable message written around the clamping ring (hub), but also sometimes there’s just an arbitrary barcode there.
If it’s bright silver colored and made before the mid-90’s, it’s a regular CD, and not a CDR. If it’s made after the mid-90’s and has “IFPI 1234” or something in tiny tiny print, stamped into the plastic, or etched with a laser around the central hub ring, then it’s a CD stamped in pressing plant (who are participating in the whole IFPI thing for tracking bootlegs/counterfeit/pirate pressings).
CDs manufactured in the 2000’s seem to be made on the same manufacturing lines making DVDs and Blue-Ray discs… so they write all kinds of stuff in the matrix (central hub) area now. Generally stuff you won’t see on a CDR, like “Manufactured by Universal Records” or “EMI Swindon” or whatever… no more obscure barcodes and cryptic “A+12” codes.
And yeah… the color of CDRs is different, and when you hold them up to the light, the amount and color of the light transmission through the media is different. The only confusing case is CDs using gold rather than aluminum (or actual silver (which can tarnish to a brown color, but mostly around the edge of the CD)) um, so gold… when CDRs use gold, they’ll be slightly greenish, or almost transparent.
The top and the bottom surfaces of a CDR will frequently be different colors. An ordinary CD will be the same color on both sides. (You know, ignoring the opaque printing on top.)
The unwritten (un-engraved) outer portion of a CD will scatter/reflect light differently from the inner written/engraved portion of the disk. It’s easy to see the difference when looking at the reflection of a point light source at an angle off the bottom surface of the disc. A CDR will have a continuous spiral from the inner edge to the outer edge of the bottom surface, so there will be no matte or glossy ring around the outer edge of the bottom surface.
Update:
I just remembered the other confusing case if you’re going by color and don’t recognize the hue of any of the azo dyes used by CDRs… Some CD manufacturers make CDs and CDRs using colored polycarbonate plastic which is transparent to infrared. Sony Playstation CDs used a “Black” (really IR color) plastic. Memorex used to sell a “Cool Colors” branded line of CDRs in a couple of bright fruity primary colors. I have some recent (circa 2015) CDs manufactured with brightly colored polycarbonate plastic. (DAT Records releases are like this.) The biggest clue is the clamping ring area around the central spindle hole will be colored, rather than colorless plastic… It’s not really possible to visually distinguish between a CD and a CDR if the polycarbonate is dyed like this, so just check if the disc has an ATIP by reading it in a CDR drive.
