Elahera chrysoberyl alexandrite: chromium-iron absorption lines and daylight color shift?

The optical color-change phenomenon in Ceylon alexandrite (chrysoberyl / BeAl2O4:Cr3+) is governed by trace chromium substitution within the aluminum octahedral crystal sites. Chromium creates a broad, intense absorption band centered in the yellow-orange spectrum (around 580nm), while leaving two distinct transmission windows open: one in the blue-green region (around 490nm) and one in the deep red region (above 650nm). When illuminated by balanced daylight (rich in blue-green wavelengths), the stone transmits green; under warm incandescent or candle light (rich in red wavelengths), the red transmission window dominates, shifting body color to purplish-red.