We have been making up new wholesale sample packets. Each one contains a butterfly mini-skein of about 12 yards of undyed yarn and wrapped in a sample of the same yarn which has been dyed and dried. This allows our customers to see the difference between the natural and finished yarn.
On Ravelry one of my customers has started to show several shots of her overdyed yarns. She loves to use a mild solution of black dye liquor and has achieved some beautiful results. Here is a shot of my first overdye experiment on Sheila's Sparkle. The yarn on the left, Cash DK 50/50, was dyed with Sparkle in the same pot, but not, of course, ovedyed.
My new colorway looks like the greyed down 50's aqua tones to me, and is OK, but not fantastic like my customer's work. I'll keep trying.