This stone is nearly black and therefore will exhibit virtually no color change. Do you see how bright the light has to be in order for the stone to show any color? You can't even distinguish the fingers from the wall.
As others said, this stone will be black. Hard to say if there even is a color change.
If shining a bright flashlight point blank translates to = black stone color changed to blue...not sure if that counts
The image where the stone is "purple" looks like bad photo editing. Notice how the color of the whole image is totally different and much more saturated / orangey