Have to confirm Matts words. If you go technical, there a lamps on the other side of your screen that are emitting light independently of the colour on your screen. Between those lamps and your eyes is a layer of LCD that stops some of the lights & the screen changes its colours.
As for the APIs, if you need custom seacrh - go on & change CSS for your custom search on Google to black
. Add some JS and change their logo (I never said it
). Other Google services works the save way - you can change anything, just make some investigation!