AMMO by MIG Pigment Set. - Fine Pigment Powders for Modelling
Colors: Pigment Rust Set

From the Manufacturer:

The pigments set you need to give your kits the rusty look you want. It includes three tones; an orange pigment for fresh and recent rust (A.MIG LIGHT RUST-3006), a darker tone for older rust (A.MIG TRACK RUST-3008) and a medium toned rust color. (A.MIG -3005 MEDIUM RUST)