From the manual:
TintScreen (int red, int green, int blue)
Tints the screen with the specified RGB values. RED, GREEN and BLUE range from 1 to 100.
Pass (0, 0, 0) to turn off the tinting and go back to how the screen normally looks.
NOTE: This command is currently experimental, since it causes a massive slowdown in the engine, especially at high resolutions. If you use it, you should provide an option for the player to turn it off.
NOTE: This feature only works in hi-colour games.
TintScreen (100, 50, 50);
will tint a heavy dose of red.
I think that should do it...