Would it be possible to add highlighting of tabs (anywhere) and whitespace at the end of line, similarly to how Midnight Commander does it (see the attached picture)?
mcedit tab and end-of-line whitespace highlighting
That depends on a concrete syntax, but at least for c/c++ colorer has:
<param name="tabs-as-errors" value="false" description="Shows tabulation symbol as error"/>
<param name="spaces-as-errors" value="false" description="Shows trailing spaces as error"/>
you can change these params to true and colorer will highlight the desired regions. In eclipse and latest farcolorer you can change this in UI dialog, or, you can just hack it in proto.hrc