In vanilla R, you can change the font colours quite easily.
Go to Edit and then GUI Preferences ....
At the bottomleft, you'll find options to change colours for the following:
backgroundnormaltextusertextpagerbgpagertexthighlightdataeditbgdataedittextdataeditusereditorbgeditortext
Select one of them and then you can choose the appropriate colour from the option Console and Pager Colours in your right.
But like Chris, I also don't have an answer, if your question is on RStudio. You can try different options provided in the Editor theme, though.
NOTE: This post is actually same as your earlier post here. Should these two topics be merged?