I upgraded to Ubuntu 14.10 today, and in its version of gedit (3.10.4), the spell-checking plugin highlights misspelled words in light grey. Is there a way to change it back to red? I poked around the Color Scheme Editor and couldn't find a corresponding style.
This is not really an answer to the problem, but a quick trick:
change the set of colors used by gedit in the preferences. In some sets the light gray is clearly visible.