The techniques involved in all of the above take practice and
dedication to make them look presentable. Any nitwit can slather on
stains and glazes in different amounts to show dimension, but true
accenting is different.
I would start with any books from Dresdner
to get the ball rolling. There are other good books out there as
well, and all of those guys have more than one out.
As far as shading and toning go, you should look into the great stuff
some of the luthiers are doing. A three toned sunburst guitar is a
thing of beauty, and some of those guys are real masters at designing
and creating those finishes.
The basics of the guitar wood coloration (for the purists, I did not
say finishing) is no different than any other wood that you shade,
tone and stain, etc.