Examination of recently introduced greenish yellow to yellowish green HPHT-treated diamonds from three companies revealed several identifying characteristics. Gemological properties include a highly saturated body color, well-defined brown to yellow octahedral graining, moderate to strong green “transmission” luminescence to visible light (associated with the graining), and visual evidence of heating. Most of the treated diamonds, including some from each of the three sources, exhibit chalky greenish yellow to yellow-green fluorescence to UV radiation (long- and shortwave). Distinctive features seen with a handheld spectroscope include a 415 nm line, a strong band from about 480 to 500 nm, a strong line at 503 nm, and emission lines at 505 and 515 nm. IR spectra reveal that they are type Ia diamonds. Near-IR spectra show a peak at 985 nm, an indicator of high-temperature exposure. A small number of these HPHT-treated diamonds are yellow to brownish yellow; they do not show any green transmission, but other properties identify them as treated.