Anti-Aliasing on white text causes green outline

[Ofnuts]

Known problem... This is due to the library Gimp uses (libcairo) using sub-pixel rendering when it shouldn't do so. Two workarounds:

1. disable sub-pixel rendering at the system level (this is some option in your desktop settings, for KDE it is a sub-option of "Fonts>Font>Use Antialiasing". Whether you can live without it is up to you
   
2. fix the problem when it appears (it is visible mostly for white text over a dark background), replace the text layer with:
   •  Layer>Text to path
     
   • Select>From path
     
   •  bucket fill the selection.
     

Now, Gimp was never meant to be a text processor. If you need goo text support, see Scribus... (or even some LibreOffice component (Impress/Draw))