What is the optimal combination of text and background color for EEG experiments?
Are you trying to measure something specific to the stimulus you are presenting or is it just a matter of displaying text on a screen where what you are measuring is unrelated to the text per se?

For instance, experiments I run depend on the stimulus presentation. We are targeting a certain visual pathway, so for example one stimulus is red/green and high contrast, the other black/white and low contrast, both on a black background. We have also run on a grey background as that can be easier for the eyes. And we also have dim lit rooms, to help amplify the signal or even lights off. Also, the stimuli are flickering at a high rate so we use a LCD monitor with a refresh rate of 120hz. We used to use CRT monitors though as the black color is blacker there then newer monitors.

It just depends on why you need to optimize it. Is it for a true signal you are recording? Or simply comfort and ease for the participant?

If it is simply for comfort, I would recommend no color, but grey background and black letters, and dimmed lights. If the contrast is too high, such as black background and white letters, this could be a strain to read over time. There is no gold standard. It's according to what your needs are.