Yeah it amazes me as to how they knew which stone had colors. I am learning the different stone types. The ones unworked. The gray to white ones are blue gray inside, The tan ones are black inside, the quartz are white inside and the yellowish ones are banded inside usually yellow with black likes. And some are pink if the cortex is white but a chalky feel to them. There is some that are brown cortex but red inside. I look at everything even the flakes and debitage. I find it all interesting. Thanks for the comment.