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I figured that it is probably having to do with the wavelengths of visible light that are absorbed and transmitted by the ions, but I'm not entirely sure.


marked as duplicate by Curt F., Klaus-Dieter Warzecha, bon, Jon Custer, Todd Minehardt Jul 20 '16 at 13:30

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  • $\begingroup$ Your assumption about the absorption of light at different wavelengths is on the right track $\endgroup$ – Technetium Jul 20 '16 at 6:34

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