Shirt color
Or MAYBE, just maybe...
Indy packs more than one shirt when he goes somewhere!
Wouldn't you?
Also, remember that Indy does not wear a uniform, where everything MUST be perfect. He wears a STYLE, a style that was very popular among men of that time period who'd been to war or had done a good deal of blue-collar work. Khakis can come in a variety of shades, and ALL are accurate in terms of the SPIRIT of the style of Indy, and all the other working stiffs in the Depression Era and WWII, which is kind-of what Indy reflects. Also, MOST clothing was of earth-tones or basic blues until the '50's. Only then did we see much more variety in terms of colors in clothing, along with different fabrics. Up until the '50's, most working men dressed in either khakis, denims, or chambray shirts. Undershirts (wife-beaters) were common, but T-shirts were still mostly seen primarily among those in the Navy.