The only overdyed threads/floss that I have found are Weeks Dye Works! If you contact their customer service, they will convert other overdyes to their colors.
I am another older stitcher and I get VERY angry when floss is labeled colorfast and then, on the back side of the label one can read that they recommend rinsing in hot water and blotting on a white towel to see if dye bleeds and repeat this until clear. Another company has one wash and rinse and rinse and rinse (you get the picture) until not bleeding. And, remember, floss should hang to dry after toweling as dry as you can get.
I want colorfast to mean colorfast. I hate losing 1-2 days of stitchy time to preparation of floss. I think it is cheating customers to say one thing and mean another! So there!