Pettsons site is out of the air for a long time.
I have all the Husqvarna books at home. If you need some info I can look it up.
Husqvarna had a restoring service in the 1980's. And it might be that the color you're referring to is from that period. As far as I know it is not a cyanide hardening but the carbon case hardening. Post some pictures and I can tell if it's original or redone.
There is some information on my website, but not much. I have to put more time into it, but that's the problem.
http://www.weiss-trading.com/HVA/