Jadeite changes because light travels through it differently.
Jadeite may look different in person because its colour is affected by lighting, translucency, surface polish, surrounding reflections, skin tone and even camera processing.
Unlike a painted object, fine jadeite does not simply sit there as one fixed colour. Light enters the stone, bends, scatters and returns softly outward. This is why jadeite can appear brighter outdoors, moodier indoors or warmer against the skin.
In simpler English, good jadeite has mood swings. Fortunately, the elegant kind.