is it
?

flat or deep - deep or flat

light or dark - dark or light

full or empty - empty or full

ying or yang - yang or ying

black or white - white or black

window or surface - surface or window

fore- or background - back -or foreground

something or nothing - nothing or something

positive or negative - negative or positive

thing or illustion - illusion or thing

actual or virtual - virtual or actual

screen or page - page or screen