HTK-A004 — US Olive Drab (early) — Used for upper surfaces of USAAF aircraft until 1943
HTK-A019 — Medium Green — Used for blotches on Olive Drab background until 1942
HTK-A018 — US Olive Drab (late) — Used for upper surfaces of USAAF aircraft after 1943
HTK-A033 — Neutral Gray — Standard colour of lower surfaces in all Olive Drab schemes