Pav.
Not a definitive response, but commercial CDs are stamped (a bit like LPs) and CD-Rs are produced by a pseudo photographic method.....Thus CDs are Silver, and I've seen CD-Rs coloured Green, Blue, Gold etc.
An easy way to prove what you've got, is to leave said disc in bright sunshine for a day or so.....!!If it doesn't play anymore, then it is - was (!) a CD-R!!
Regards
Ralphie