Hi

thanks for posting the example

to be honest if you have a lot of this sort of work to do then it would be worth looking at photoshop elements [trial version available - though there is a problem downloading from adobe I believe until July 1st]

one click in one of the affected areas with magic eraser ['contiguous' setting unticked] will turn all the affected areas transparent both with within and without of the letters - then a second click with the paint bucket tool [also 'contiguous' unticked plus foreground setting white] in one of the transparent areas will turn all of them white

if the areas of coloration vary significantly - it will be that much more work, whichever way you end up doing it - still worth looking at photoshop elements I would have thought, just end up doing more passes whichever program you use

David has covered the equivalent in PSP

it would be worth looking at the scanner settings too if there is more of this work to do