The color of this common, medium to large, smooth-scaled, slender, snake is uniform but variable — from olive, tan, brown, or blue to gray or nearly black. The belly may be yellow, cream, or light blue gray. Juveniles are tan, clearly marked with closely spaced gray or brown blotches and spots in the middle of the back, and smaller, alternating spots on the sides; the belly is usually cream colored with dark gray speckling. As the young snakes grow, the markings fade and eventually disappear by the third season. When alarmed, racers try to escape quickly and sometimes vibrate their tails. When captured, they struggle violently, bite viciously, and discharge musk and waste matter from their vents.
Similar species: In southeastern Missouri, the eastern subspecies is replaced by the southern black racer subspecies (Coluber constrictor priapus), which is usually uniformly dark gray to bluish black and has a prominent white chin.