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The copper phthalocynanine dye in the "Vanish" should have an absorption band centered around 630 nm, with half-widths of about 20 nm.

An interesting variation is to show the absorption peak using lasers.  In picture # 3 above there are 3 laser pointers.  The top laser pointer has a wavelength of 650 nm, the middle has a wavelength of 633 nm, and the bottom (green) has a wavelength of 532 nm.  When a "Vanish" solution of the proper concentration is placed in the path of the lasers the 633nm ( middle or He/Ne wavelength ) is absorbed.