Nigrico, nigricas, pe. cor. nigricâre. Plin. To be somwhat blacke.Nigricans color. Plin. A blackish colour.
Lewis and Short: Latin dictionary
nīgrĭco, āre, v. n. [1. niger], to be blackish (post-Aug.): epimelas fit, cum in candidā gemmā superne nigricat colos, Plin. 37, 10, 58 fin.; cf. Not. Tir. p. 128.—Hence, nĭgrĭcans, antis, P. a., blackish, swarthy: Tyrius color nigricans aspectu, Plin. 9, 38, 62, 135; 36, 26, 66, 193.