How can I customize all display colors?

[fduniho]

Since I use my MP3 player during the night, I have customized the background and foreground colors to not include any blue light. My background is black, and my foreground color is orange. Despite this, I still see blocks of text appearing on the screen that appear to have a white or pale blue background. For example, if I have nothing to resume, and I select "Resume Playback", it pops up a message saying "Nothing to resume", and this has a white or pale blue background. What can I add to fixed.cfg to control the background color of these popup messages?