I am using this logic as well. I might mildly dye the blue Orvis shirt with a bit of grey, just to make the shirt look a little more worn and distinct but even that I'm not sure about, yet.
Because I won't have the exact same pants from the movie, I worry about wearing a grey shirt with grey pants and how that might look, if the shades of grey don't have the "correct" contrast or are too close to each other, or whatever. And I just like how the blue shirt and brown vest complement each other.
As for pants, after looking at/trying on some options from
Dickies and
Levi's, I am going to wear
Denizen 216 jeans in "Gargoyle" color from Target. Mainly because:
a. I don't want to spend too much on the pants for this costume since I anticipate dyeing/weathering/dirtying them up a bit,
b. they have a good, even coloring so they don't necessarily look like typical denim, and
c. Denizens are my usual everyday work/casual jeans (albeit in blue) and they are comfortable (they have a slight stretch to them) and fit well for me as well as looking true to the character, with the slim and straight legs. They're listed as $29.99 on the Target website but in the stores right now, they are marked down to $19.99. Just in case anyone was interested!