Usually found as a bright middle yellow, PY154 is one of several benzimidazolone yellows, and in general comes highly recommended for lightfastness. PY154 is a famous benzimidazolone yellow that is an alternative to Aureolin (PY40, also known as cobalt yellow) as well as other more modern yellows, such as PY73, a Hansa Yellow. Benzimidazolone Yellow, PY154, tends to have far better lightfastness than the other yellows which it is able to replace. While perhaps not perfect, the lightfastness of PY154 is rated very highly, and artiscreation lists several sources that show all 8's (highest marks) on the Blue Wool Scale for lightfastness testing. Golden chose PY154 to replace one of their other yellow pigments, as described in this article. In Schmincke's watercolors they assign it four out of five stars for lightfastness, with five tending to describe the bulletproof lightfastness of some of the earth tones, so a four means very high in lightfastness. While this color is often more of a pure "primary" yellow, we've also encountered it as a deep yellow-orange, so the color may vary a bit. In terms of health, Monona Rossol's work notes that the chemical in PY154 may metabolize to create something that causes or is related to causing methemoglobinemia.