I discussed this recently with Robin Brown of AA Brown. He is, in my opinion one of the very best at colour case hardening, though not as lauded as the St Ledgers.
He did a gun recently for Vic Venters. Now, Vic did not want case colours. Robin told him he needed them Vic does not like the thick, dark colours as he thinks they hide the engraving.
Robin explained he could colour it lightly and cut the colours back to allow the engraving to show through, with a skin of fine colour showing it at its best.
I think Robin got it spot on - Vic agreed!
Following on from this, Robin showed me a gun (a barely engraved boxlock) he was restoring. The bare action looked rather sorry for itself amid the other surfaces looking all nice and sharp. Robin very subtly put some light colours on, which were not as in your face as a lot of what you see. He was able to get the balance right. So, Eightbore, I read your 'in the white' to be a cleaned-off old action, rather than an un made-up one which you are bringing into service from new (correct me if I got this wrong). So, if you plan to colour it, I'd recommend the subtle route. Just my opinion.
On the subject, I recall a lovely Woodward hammer gun in very un-messed condition which I lost a bidding contest with a UK dealer for. It made about 4,000. I saw it for sale at a Game Fair a year later, fully done-up and re-coloured. To my eyes, he had killed the gun. Asking price was 9,950. Someone bought it - maybe it was Mike Campbell!
I have my way of doing things, some appreciate it, others have their own ideas.
