Conestoga has a website that has sample woods and stain colors on it. You click in a type of wood and then try different stain colors. Not sure this will help you but you can try. Google conestoga finishes.

I'm trying hard to envision what you mean, Christine.

Like this p[iece from Restoration hardware? Which is gray, but dunno about brown.

All I can think of with "brown + gray" is reclaimed wood, a la:

I suspect you're not really the type for rustic finishes, otherwise I'd say milk paint might be the way to go, since it can give you that translucent gray that still shows some of the wood. Alternately thre are some excellent dyes/stains available that simulate weathering effects on wood:

Here is a link that might be useful: you can get good quality driftwood stain from modelers, of all things