I'll guess the shaft was cleaned with bleach or something that contains bleach. That yellow-green color is characteristic. A few years ago I used Softscrub With Bleach on some shafts and on an unfinished curly maple butt that I had brought to the poolroom to test-hit and stained it with chalk. With time, after I "cleaned" it, the butt turned almost florescent yellow with a hint of green. So did the unfinished portions of the shafts. Hideous. On the butt, the yellow happened after I finished it...it looked like a leopard.
Sanding fixed it but the staining was fairly deep.
Just my guess. I'll never forget that yellow-green color.
Edit: Yes, a LOT like a highlighter!
Robin Snyder