Please excuse this seemingly dumb question....is the stone actually blue/violet or is this lighting
That's a really good example of mixed lighting. The blue stone is exactly the same color as the material behind it - but the foreground is illumined by the blue sky of dusk while the background is lit by incandescent lamps. Unlike the human eye, cameras don't easily subtract out the color of lighting. At the very top it is lit by a fluorescent lamp with its distinctive green color.