It seems that using this tweak with cheap CD players gives big improvements.
Ric Schultz at Electronic Visionary Systems just modded the Oppo 970HD for me (for $800--its sounds super, by the way). Part of his mod blackens the Oppo's tray (which by default is clear plastic) with permanent marker to improve optical reading of the disc.
Codename Turquoise is really closer in color to the green side of the Marigo Signature cd Mat, and operates on the side opposite the Marigo. The Marigo mats have consistently garnered compliments for the perceivable improvements they bring to the listening experience.
I also sand the inner and outer edges of my cds, blacken them with permanent marker and treat both planar surfaces with Auric Illuminator before playing. I suppose that disclosure will elicit more guffaws from the local "gallery of disdain" having congregated on this thread like eaters of carrion, but so be it. : )