EDIT: Errant, that is almost EXACLY what this shader does.
I have four different sepia tones you can add or mix with color in any amount. One of my favorite is washing out the color and adding a slight blue tone shift. It makes it look like old WW2 footage - great for setting the mood.
I'm proud of this one. I'm surprised how much atmosphere it adds when playing a game, even at subtle settings. Almost makes you forget it's a game.
Plus, it makes everything look more integrated. Especially when you have models from different artists with different styles. It homogenizes the color, disguises hard, low poly models, and even disguises bad texturing.
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"bond1 - You see this name, you think dirty."