Blue: Reflex Blue or 286 (Reflex Blue is directly above 286)
Purple: 2597 or 527
Green: 356
Most probably I would go for Reflex Blue, it's dark enough not to be obtrusive when reading. Keep in mind that red color means danger and human eye&brain company is especially tuned to look for it.
Oh, and please, don't do the same mistake as many companies, eReader surface should be anything but reflexive - you don't want to reflex light to user's eyes and eReaders will be held all the time when used, reflexive surface looks much worse with all those fingerprints. Gleamless surface would fare much better. I am sure you know that, practicaly anyone should know that, but still there are tons of devices in computer industry released every month with reflexive surface.
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