Design AtlasA projector never renders true black, and a room with mixed ambient light makes the whole screen look a shade brighter than it should. Contrast that looked plenty strong on your monitor can drop by half or more once it hits the actual screen.
The demo layers the same bright-light effect — a translucent white wash — over both versions. The ✕ (pale yellow text on a light background) nearly disappears under it, while the ✓ (bold white text on a dark background) stays clearly readable under the exact same wash.
Checklist: does converting the slide to grayscale still show a clear difference between text and background — a quick contrast check, has pastel or light-gray text actually been tested under a real projector or bright room, does important information use weight or size differences and not color alone.
When to use
When a venue or lighting condition is unknown in advance — an outside hall, a daytime conference — design for extra contrast rather than less.