There is always a danger in seeing what you want or expect to see in a pale colored stone with tourmaline. Many to most tourmalines have two colors (a/b and c axis) and those colors can be quite sensitive to lighting. Now this shouldn’t be a problem with a true Achroite, which is colorless because it is so pure”. (This is a set up)
Now when I saw a picture of the rough that became this delightful stone of 2.17 carats, I did not see any color in the picture. When I received the rough, I did not see any color, but it had been advertised as a blue/purple, which made it irresistible to me. When I cut it into a simple standard round brilliant, I did not see any color. The lack of color even helped the clean stone to be very bright and flashy. Again and again, no color,let alone blue-purple, in the stone. This was not particularly pleasing to me, so as I was commenting on the gemstone, I asked others to see what color it was. They saw fleeting hints of blue-purple. (I guess the rumors that the seller was partially color blind or had my number were premature.)
Can this conundrum be resolved? Well here goes. I have read that they have instruments that can see into the eye so clearly, that they can count individual light sensors (rods and cones). The ratio of the three different colored light sensors (cones) appears to vary a lot even with “normal” eyes. I have seen this difference in personal color perception, effect the line between yellow and green and red and purple, a lot in tourmaline. Your color perception tends to also yellow with age. So my old worn eyes were not up to the task here, but I wanted a more “scientific” answer.
Now about four years ago, I purchased a small spectrometer to test my collection for copper in tourmaline and whatever else I could find. I found quite a few cuprian tourmaline that I did not know about and even some other gems, like an iolite and rhodolite, that did not belong. It was fun using the spectrometer and when I work out some problems with light sources, I intend to do more work with the tourmaline. When I used my “toy” on the wayward “achroite” that MAY be purple blue, I got a wonderful classic absorption curve of a cuprian tourmaline! So my eyes have been shot down for sure. But since I am the head honcho with this collection, I still call this copper bearing tourmaline an achroite, because that is still the way I see it.
UPDATE, MAYBE EVEN A FLASH
Some tourmalines and their colors that they show continue to amaze me. The following is a true story, where no names have been changed to protect the innocent. My younger daughter Audrey lives in Key West with her husband who is in the Air Force. They were back for a high school reunion and to say good bye for while, because they are moving to Okanawa. I was driving them around and felt it was a perfect time for her to see some of the tourmaline collection. What she likes and sees is always interesting. As I was driving she comment on some and asked questions and then I noticed out of the corner of my eye that she was looking closely at the Achroite in this post. Why I asked inocently and she said that it had a sort of gray blue purple color that she liked. She held it over and on the windy road I took a quick peek and sure enough I could see it! Of all things with this stone! I am back home and looking at the stone. It is showing me the bearest hint of color in the shadows of a setting day. All I can say is that Audrey liked it and picked it out of 100 of some of the best stone in my collection. That is pretty good for me no matter what this gemstone really is.