Color replacement: more complete control

[joema]

I have a scanned .jpg image of a geographic map which has grey smudges dispersed widely across it. See attached.

I've tried clone stamp, color replacement tool, and healing brush. They work, but require a lot of panning, zooming and changing brush sizes.

See attached image. I want to replace the grey smudges with a white background, but not replace other map features.

It seems this would be possible by:

(1) Replacing colors in a user-specified region, AND

(2) Limiting the replacement to a USER-SPECIFIED +/- tolerance of color BASED ON THE TARGET. IOW sample the target region to be replaced, and only perform the replacment if the target is within a user-defined % of color, hue, etc.

It seems the current color replacement tolerance control compares the source to target, whereas I want to specify a +/- tolerance based on the target itself.

Do I misunderstand, or is there some easier way to do this?

Thanks for any advice.

Using PSE 6.0