Natural type Ib diamonds are almost always brown, yellow, or orange, whereas their artificially irradiated and annealed counterparts are usually pink to red. HPHT treatment can produce yellow in an off-color type Ib diamond. HPHT processes may enhance type IIa brownish diamonds to appear colorless or pink,
and may produce blue in some type IIb diamonds. However, HPHT treatment cannot alter a type Ia diamond to colorless (except rare pure IaB), so if a gemologist determines that a colorless diamond is type Ia, it is usually not necessary to send it to a gemological laboratory for further testing (the few colorless syn