Tamiya Weathering Master D (Burnt blue, Burnt red, Oil stain)

Burnt Blue (for scorched metal look)

Burnt Red (for scorched metal look)

Oil Stain (for realistic brownish-gray oil stain color)

Easy Way to a Pro-Level Finish
Weathering
means adding realistic-looking effects to your models, such as sand on
tank treads and mud-caked rally car bodies. These new Tamiya Craft Tools
offer by far the easiest way to achieve realistic weathering effects.
Weathering Master comes in a pocket sized case with 3 colors and special
applicator tool. The pen-type Weathering Stick offers up to 5mm of
easy-to-apply color by simply twisting the tip.