You could always park a MOW train over the errant section, and include a ballast car loaded with the offending color... ;D
Is the new blend too dark? too light? do you think it's something that could be blended with some weathering washes, or perhaps a thin application of some ballast that's closer in color? You could get some cheap colored sand from the craft store and monkey around with it to see if you can get closer...
That's one area where Woodland Scenics has the edge. The stuff may be difficult to work with and way too chunky, but you can always find it!
Lee