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Light passes through the dye layer to the reflective layer and back out again for recordable optical discs. The simulated "pits" are spots that are where the dye is burned to prevent light from passing back out. The important part of the mark is how well defined the edge of the burn mark is, just as it is the edge of the pit. (The reading laser gets data from the changes in reflected angles when it hits the edges of pits/marks, not the pits or marks themselves.
CDs and DVDs have no dye. The light passes through the clear polycarbonate until it hits an aluminum mirror layer, then bounces back. That's true for both lasers and the human eye, but the human eye reads all wavelengths of light passing through the plastic. The light from a laser is a single wavelength. CD-R dyes can be deep blue (azo-cyanine), blue-green (cyanine), or faint yellow-green (phthalocyanine). All these dyes are tuned to react to a laser burning infra-red wavelengths, and the reflected light bounces off a layer of silver alloy or gold (aluminum corrodes in the presence of these dyes). DVD dyes are cyanine, azo-cyanine, or oxonol; and they all look deep purple to our eyes when visible light bounces back from their silver alloy layer (gold is less reflective and much more expensive). They are tuned to darken when burned by a laser at "ruby-red" light wavelengths (generally 635 to 650 nanometers.)
"Colored" discs use a tinted polycarbonate to look different. The "black" discs use a very dark red/purple color that lets so little natural light back that the discs look black to our eyes. To the laser with its single wavelength, the light passes right through the "black" and all other colors except green--green aborbs red light.
In short, it is the dye that gives the discs their color unless the polycarbonate is also tinted for a color effect. CDs and DVDs have no dye. You are seeing their aluminum mirror layer, and that is why they look silvery.
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