re: Walnut

I don't really have one. 
I look at each job differently.  Depends on what they want.  
I do have enough experience to know if I can achieve the color with MinWax, 
or if I have to make my own with mineral spirits, tint and blo,  
or just go to the SW and have a color match made.
A lot of times I buy the small cans (whatever brands closer to what I'm after) and mix and match to see if I can get it close. Then go buy the big cans and replicate it.
Stain matching can be an art.

PS,  I have thrown a lot of stain ($$) away because of not being right.
Or keep them around for the one job that doesn't really matter,  which almost never comes along.