Invulnerability colormap bug

When a player becomes invulnerable, the colors in their display change to inverse monochrome. In Vanilla Doom the sky retains its original color; long thought of as merely a property of the invulnerability power-up, this was found to be a bug after the release of the source code.

Demos
[[Media:e3m6icb.lmp|The invulnerability colormap bug]] on E3M6: Mt. Erebus