The color change you see is actually due to an "inactive" mask for buttons that can't be pressed, same one which causes other icons to be greyed out.
What are the steps to reproduce it?
Could you send us a sample (a snapshot) of Path Finder process in a separate file? This will enable us to analyze what happens with the application. Here's how to get it:
Open Path Finder and reproduce the problem. If the problem is dynamic (e.g. unexpected action result), please try reproducing it during the sample collection.
Open Activity Monitor from the /Applications/Utilities folder.
Select Path Finder in the process list. To help making a selection, type "Path Finder" in the Filter field.
Click the Sample Process button in the toolbar - this will open a new window entitled "Sample of Path Finder" and a sample of the process is collected.
Click Save and save the sample file.
Close (Command-W) the Sample window opened in step 2.