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.