I have created two new variants to the UP and UP Snoot SD40-2s from Searchlight Simulations, both color faded and weathered versions. The Faded are just simply color faded so that they are not so bright and clean, while the weathered version has grime and rust added for extra aging. These engines will look great accompanying the UPN locomotives on your modern scenarios to give added variety. They are also great for branchline use where you might typically see an older engine being put to use.
http://www.mediafire.com/file/bs4gapeomkaosoq/JRSD40-2_UP_Weathered.zip/file