We're rockhounds, and there are MANY rocks formed in nature that are porous and will absorb dye...and have various holes, pits, cracks, and anomalies throughout the stone that would allow dye to seep into them and color them from the 'inside out'. And many rocks have varying hardnesses & porosity...some in layers, some are like eggs...hard on the outside, soft on the inside...and some are vice versa, and some a mixture of both - or any combination of all of the above.
That would allow for a rock (or stone produced in the body) to be slightly colored on the outside (or hardly colored at all), and yet brilliantly colored on the inside...or virtually any combination of color one could imagine.
But no matter how the rock was colored or affected by a dye, it certainly wouldn't determine what country it came from, eh? :)