In an article on pipe restoration written back in 1993 for Tobak News and Views, the official publication of The Pipe Collectors International, I recall that the author indicated that he used leather dye: light tan for brown finishes, maroon to match Bruyere or Belevedere, and a mixture of maroon, navy, and black for Shells. He also noted that he diluted the dyes with grain alcohol in a three-to-one ratio. If memory serves, he also stated that he "burned in" the color by igniting the bowl immediately after the dye was applied, a process that he repeated twice, allowing the bowl to dry thoroughly between coats.
I have used Fiebing's leather dyes for years, and have always been pleased with the results.