The color depends on the map, but the most flexible colors are white and black. They can be used like 2 sides of a coin. For this I used Black because only the cold maps are white. You want to get the largest decal you can get. I used carbon as it is literally just a big circle. Cover the center most part of your mech or the most obvious part of your mech. This will make it more indistinguishable from the surrounding terrain. Allowing the enemy to look past your mech. This is most effective when you are standing still. If you are black on a cold map you will need to hug surrounding structures to for enemies to assume you are part of a shadow. If you find a big enough one that is. Images below.
I like to use Broken Heart Decal with Black Camo color. Make sure to rotate the heart so it is not easily noticed. Works well with many camo patterns for covering missile pods or cockpits.
Good call on the ppcs, though i love their cyan aesthetic I personally just like using nice colors and my decals for my personal battlefield tag
Well, now that Stealth Armor is a thing it's more important to try and blend in. It's hard, though, because about half the maps are snowed/frozen over and need an entirely different camo scheme. At least urban and woodland camos have a good amount of overlap...
Stealth armor is only good for brawlers. Mid range, long range use up too much heat and + it doesn't show what you need to shoot on the minimap. Ecm fully skilled out is stealth armor, just with a minimum range. (Stealth armor can be cancelled.)
I can make an exception for the few mechs in my garage that use Stealth Armor (pirates bane, maybe a ctf 0xp soon)