purpŭrasco, ĕre, v. inch. n. [purpuro],
to grow purple , become of a purple color : unda cum est pulsa remis, purpurascit, Cic. ap. Non. 162, 31 (Ac. Fragm. 2, 7 B. and K.).
purpurāscō —, —, inch.purpuro, to grow purple : unda purpurascit. ...
An Elementary Latin Dictionary