One quick way to eliminate a color cast is to identify and set the gray point. Once you've identified the gray point, you can use either a Levels or Curves adjustment layer to set that point to gray. Here's a good tutorial.
As in all thing Photoshop, always different ways to get you where you want to go...
Used camera raw to adjust exposure, vibrance, and curves (adjusted each channel separately)
Then adding a blank adjustment layer above, set it to color, choose a brown area with the eyedropper tool,
then using a brush, go over the purplish dirt areas you want to change
(*You can skip above, use eyedropper tool to pick a brown color, choose the brush tool set to Hue, then brush over purplish areas
Add a curves adjustment to bring out your color and brightness)