Two instances of ColorDelegator are in the percolator chain. This is a regression from 2.x.
The problem can be found in __init__ of EditorWindow in EditorWindow.py.
Calling "io.loadfile" eventually calls "filename_change_hook" (See IOBinding.py's "set_filename"). The "filename_change_hook" calls "ResetColorizer" which brings up an instance of ColorDelegator. Then, the self.color reference is overwritten by a new ColorDelegator instance and added to the percolator chain.
The attached patch fixes the problem.