[NTG-context] comparing text with the new typo-dif.mkxl

Hi Hans, from typo-dif.mkxl, lines 16-17:

% Currently only a color can be set but I might add support for underline % and simple background.

Would it be possible to have simple (color) background implemented? After comparing texts, I realize that when few chars differ (or even only one), it is harder to notice. Colored background (with even white foreground color) is far easier to notice. Many thanks for your help, Pablo