It may be possible to dye it with a disperse dye. These are available from most dye suppliers.
Make a dispersion of the dye into water, heat to near boiling and put the parts into the heated mixture. It may take a while.
Alternatively, coat the article with a thin layer of this dye and bake it (with ventilation). You'll have to figure out the times and temperatures. A hot, short stay in an IR oven might do it.
Bayer sells a product called "Aura" which is designed to color plastics after they're made.
I don't know if any of these will work with Delrin. Good luck.