Back in the late 70's early 80's I did a lot of colour prints from B&W negs, I had it down to an art, 15-20 mins roughly for a print on RC paper far longer with FB.
I used a combination of toning and hand colouring using retouching dyes, but I also use chromogenic processing, I'd bleach part then re-develop in a C41 developer with an added mix of colour couplers. My work was commercial and I rarely owned the copyright, and so I only have a few of my own prints left, most of the work was for album covers or adverts.
Two photographers excelled in this work in the UK James Wedge, he published a book Painted Ladies, but the absoute master who I met a few times was Bob Carlos Clarke, his best work is in Dark Summer. He was sponsored by Agfa, he's the only other photographer I know that used selective chromogenic redevelopment of B&W prints.
The work of these photographers looks like colour originals, there's no trace Marshall Oils or Crayon smeared on the images, this is perfection.
For a rough guide to what I mean
look here, there are some links to images during the process, they were made during a live demonstration/lecture over 20 years ago.
Ian