Area-based screen tint

Legend has it, in American films and TV, scenes taking place in Mexico always have a sepia color filter on top of it. Now you can bring the Mexican Filter to your own maps!

This example demonstrates three things:

1. How to use env_fade's "Modulate" and "Fade From" flags to create a color overlay (tint) effect on the player's screen
2. How to make the effect stay on for as long as the player remains inside a certain area
3. How to make the transition in and out of the tint smooth(er)

Explanation

The tint effect is achieved by having an env_fade (screen_tint) repeatedly triggered by a trigger_multiple (mexico) covering the whole area it's supposed to affect.
Both the fade's "Hold Fade" time and the trigger's delay before reset are set to 1 second, so the fade gets retriggered every second while the player stays inside the trigger.
That would be enough for a continuous tint that fades away when the player leaves the area, but if you also want it to fade in smoothly, it'll need a more complex setup - especially if the player can move freely between areas like in this example.
For the smooth transition, I used:

• A second env_fade (screen_tint_start) with "Fade From" disabled
• A second trigger_multiple (mexico_border) at the threshold between areas with a 0.5 second delay before trigger
• Two pairs of trigger_changetarget, named change1 and change2

When the player crosses the border, this is what happens:

• The threshold's trigger_multiple, mexico_border, targets the pair of trigger_changetarget called change1 after a delay of 0.5s
• Meanwhile, the area's trigger_multiple, mexico, targets screen_tint_start, as that is its initial target
• The change1 pair activates, making it so mexico now targets screen_tint every second from now on, and mexico_border now targets the change2 pair
• If the player walks back through the border, mexico_border will now trigger the change2 pair, which reset both mexico and mexico_border to their initial targets so this whole sequence can be repeated

Possible uses

• A room that fills up with toxic gas, that the player has to escape from
• A portal that shades the player's vision greener and greener as they approach
• Simulating a "psychic attack", like that scene with the Advisor in Episode 1
• Recreating your favorite episode of Breaking Bad

Notes

• Going in and back out through the threshold too quickly will break the effect; find a way to slow the player down, or don't let them back out the way they came in
• Probably there are better/simpler ways of achieving this effect, so experiment!

Lastly, I'd like to thank you fine people of TWHL, I wouldn't have learned so much about mapping without the resources and information available here. You guys rock!

-- Mota