FAQ - How do I make the initial PTB window black instead of white?
Q: How do I make the initial screen black instead of white?
A: When PTB is first loading (running it's various checks, etc) it fills the screen with a white window. This can be a problem for experiments that involve dark adaptation, or eye tracking.
To make this initial screen black instead of white, add this call at the beginning of your main experiment code:
Screen('Preference', 'VisualDebugLevel', 1);