The env_fade entity, when triggered, gradually covers the screen with a single-colour overlay. Typically used for fading a scene in or out.
Name (targetname) - Name is a general attribute used to identify entities.
Duration (seconds) (duration) - Sets how long the overlay should take to fade into its full effect.
Hold Fade (seconds) (holdtime) - Sets how long the overlay should stay on the screen at its full effect before turning itself off.
Fade Alpha (renderamt) - The maximum alpha value (opacity) of the overlay. Scales from 0 (transparent) to 255 (opaque).
Fade Color (R G B) (rendercolor) - Sets the color of the overlay.
Fade From (1) - If enabled, the overlay starts at the maximum alpha value and goes in reverse. (Essentially changes it from a fade out to a fade in.)
Modulate (2) - If enabled, the env_fade will use an alternative rendering mode for the overlay. Multiplies the color of the overlay against the game scene. (Essentially recolours the scene rather than covering it with a solid colour.)
Activator Only (4) - If enabled, the fade will only affect the player who activated it.
If Duration is set to 0, the env_fade will not do anything. If you require a sudden overlay, set Duration to a very small amount such as 0.1.