I'm bat-eyed when it comes to colours so can't help with that discussion except to say that any of the many software programs that restorers use for their work would be suitable for colourising. I think several people on here use different versions of Photoshop or Photoshop Elements and Gimp (a free but very powerful app). Just a word of caution with Gimp. Its interface is not as easy to get used to as some of the others - but those who use it swear by it. There are plenty of review sites comparing the different programs, but really it's like being a carpenter: it's not the brand of tools but how well you learn to use them.
Anyway, here's my try.
Peter