Found this thread from a while back, but unfortunately it looks like none of the three members who did professional-looking dyes have been active in the last year.
It also looks like they were dyeing PC, but the procedure for Delrin appears to be applying silicone, rubber cement, or Elmer’s glue to protect the non-Delrin components, then using hot water to open the pores. Finally, use something like Rit DyeMore for Synthetic. Haven’t found many users who have done Delrin, but looks like a few were experimenting at one time (didn’t see results posted).
Where are you when the yoyo world needs you, @Goog, @gravyoyo, & @adamantiumpops?!