There's actually a bit of science behind it. I'm sure all you scientific types will have noticed that the colors chosen are all within the spectrum used by the optical disc's laser reader. Coloring the tray can improve the accuracy of the reader's focus and reducing error count by eliminating conflicting spectra that are either too reflective or not reflective enough.
Data on using different colors on the same tray is still out, but speculation is that this schema allows the laser to re-sample a multitude of primaries if needed to reduce error count for difficult passages or inferior pressings, Painting these colors by thirds optimizes the read time based on the turntable revolutions at redbook speeds, keeping the re-samples needed to the bare minimum.
Some have experimented with paper inserts that can supposedly further optimization read accuracy using different colors based on manufacturer's and consumers real world results, optical drive brands, disc condition and age, but the jury's still out on this.
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