Purpose <p>Existing on-site color tests for cannabis (e.g., rapid Duquénois-Levine reagent, 4-aminophenol reagent) have insufficient specificity, especially in the point of distinguishing between Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and the other cannabinoids. We developed a novel Δ⁹-THC-specific color test reagent.</p> Methods <p>Cannabinoid standards were dissolved in 0.5&#xa0;mL of a 2-hydroxybenzaldehyde solution in acetonitrile (2&#xa0;g/100&#xa0;mL) in a glass test tube (solution A). Herbal samples (approximately 10&#xa0;mg) were extracted using 0.5&#xa0;mL of the 2-hydroxybenzaldehyde solution in a plastic homogenization vessel. The extract was poured into a glass test tube through a filter cap (solution B). Solutions A and B were mixed with hydrochloric acid (0.5&#xa0;mL) and allowed to react for 30&#xa0;s, after which the mixture was extracted with chloroform (1&#xa0;mL).</p> Results <p>When observing the lower layer after the chloroform extraction, Δ⁹-THC and cannabidiol (CBD) exhibited bluish and orangish colors, respectively. In contrast, cannabinol (CBN) did not show any color. The performance of the reagent was evaluated using dried herbal cannabis (<i>n</i> = 58) and other herbal materials (<i>n</i> = 13), including CBD- and CBN-supplemented herbal materials (each <i>n</i> = 2). Only cannabis samples with Δ⁹-THC levels ≥ 0.14% exhibited a bluish or greenish-blue color.</p> Conclusions <p>The newly developed reagent shows good specificity for Δ⁹-THC. The new reagent has the potential to replace existing on-site color tests.</p>