I'm not a fan of yellow-handled knives. They're an eyesore, and if dropped on the ground they can pretty much disappear in dried grass and leaves. Dying delrin is fairly easy, but results vary (maybe depending on the water used or the actual technique or temperatures).
Go to Goodwill and pick up a cheap saucepan. De-grease the entire knife with your cleaner of choice (be careful though, some solvents may have a negative effect on the delrin). Fill the saucepan about half-full with (distilled?)water and bring it to a low simmer. Add about a tablespoon of Rit dye crystals and stir til dissolved, then reduce heat slightly (to about 180 degrees F). Drop the knife in the water and stir it for 10-15 minutes. Going from yellow to black, I'd suggest dying twice: navy blue the first time, then black. When you're done, rinse the knife and let it dry, then clean and oil the knife as after any submersion.
Or do like I did: haunt ebay til you find one of the older ones with black covers. I think it cost me about $15 delivered.