In my case, this problem has something to do with KDE’s system setting. I’m running Ubuntu 12.04.1 LTS with KDE as my secondary desktop environment and has been plagued by this annoyance for months. I did some researches and find that after I changed settings in KDE’s font anti-alias setting, GIMP started to render greenish defect on the sub-pixels around the text.
Here is my solution:
KDE System Settings -> Application Appearance -> Fonts -> Use anti-aliasing -> Enabled -> Configure -> Uncheck everything
I guess GIMP 2.8 is using a new way dealing with its text anti-aliasing mechanism, which could be the same one as KDE. So if you’ve changed text anti-aliasing settings in KDE, it may also affect GIMP, producing in an undesirable result.
Hope my information is helpful.