The paper-white display of your PC is not a distraction because you can look away whenever you want, or switch to a different program to alter your view of content. But when you watch a presentation, you are being asked to keep your attention fixed for a longer period, with no ability to change the display to the next image. To maintain attention, proper visual contrast is necessary in the design.
When information is displayed from a distance, the rule of contrast is that the background should be darker than the objects in the foreground. Color theory teaches us that black absorbs all light and white reflects all light. The darker an object’s color, the more light absorbed, giving the object the appearance of greater distance. The lighter the color, the closer the object appears to the eye. In presentations, the contrast between foreground elements and background is critical.
Items in the foreground are meant to appear “closer” to the viewer than items in the background. Highway signs have brighter letters on darker backgrounds for visibility from a distance. The credits at the end of a movie are on a black screen. Even the crawl at the bottom of the newscast is a black strip with bright text.
When it comes to light absorption, black-on-white visual presentations are less effective. The contrast is opposite the norm. The data (foreground) on a black and white image — is black. By absorbing all the light, the information moves away from the eye. But the white background reflects all light back to the audience. The eye cannot handle reflected white light for very long. It’s too distracting.
Hence, use darker-color backgrounds and lighter-color foregrounds for optimal effect when displaying content from a distance.