If linseed oil is used on stocks, over many years it will darken the wood a great deal. Don't know about "black", I would have to see what you were talking about. If they were truly black, it is either not original finish, or they were in a fire! I have seen the insides of milsurp walnut stocks that are basically black, from oil absorption and it results in sort of a wood rot where the wood gets soft and crumbly in the worst cases. And since the wood is saturated, it is not repairable.
Your gun is like your nose, it is just wrong for someone else to pick it for you!