A phenomenon of some colored gemstones in which the gem material appears a different color in incandescent light than in daylight or fluorescent light.

As an example: the sapphire in these images appears blue to us in daylight and purple in incandescent light. Daylight contains a larger portion of blue & violet light compared to incandescent light which contains a larger portion of red light. This difference in intensity causes our eyes and brain to register a different color.