We know diamonds scatter the light into some colors, but this one is from an alien level diamond cutter who never shared his skill with anyone. This will absorb the light and push it in different directions and the light rays collide with each other to form a psychedelic pattern.
This stone has a unique property of color changing throughout the day, we cannot predict what color it will emit. A massive number of factors affect the property of the diamond, atmosphere light, dust in the atmosphere, Sun's direction, weather, and viewers' eye conditions, different people see different shades at the same time...
It changes its color that is the property of the stone, but the patterns are exact because of the skilled cuts and polish. The guy behind this diamond's cutting is still in shadows, not revealed. Some people call this is done by some funny aliens who visited earth... it is a mystery unsolved.