A hatchling of 240 millimeters snout-vent length was described as follows on September 22, 1962: Ground color pale olive anteriorly, gradually darkening posteriorly, marked with chocolate blotches; middorsal blotches largest averaging about five scales long and seven or eight scales wide anteriorly; posteriorly, blotches become less distinct (tending to blend into progressively darkening ground color), and width-to-length ratio increases; gradual obscuring of blotches proceeds posteriorly, until on tail they can no longer be distinguished, and color is uniformly olive; on each side, row of lateral blotches alternates with that of middorsal blotches; lateral blotches average somewhat less than two scales long, and approximately two scales wide and are of irregular shape, sometimes subdivided; farther down on sides, lower row of lateral blotches alternates with upper lateral row; this lower lateral row, approximately same size as upper lateral row, and situated at level of first scale row, overlapping onto ventrals, where it pales to reddish brown; almost every ventral scute has one pair or more of dark reddish brown spots, tending toward semicircular shape, the arc of each projecting forward, but posteriorly on body these spots become increasingly obscure, and are indiscernible on posterior end of body and on tail; ventral surface white on chin and throat, gradually assuming suffusion of pale greenish gray posteriorly; eye dark with narrow yellowish margin around pupil; top of head grayish olive, mottled with faint and irregular dark markings; supralabials whitish, with chocolate markings, mostly wedge-shaped, in their posterior parts; rostral and internasals edged with dark posteriorly; posterior upper corner of loreal and adjacent corner of prefrontal dark; temporals having dark markings; chin almost immaculate, but with narrow black posterior edges on some of the infralabials (see [Plate 19, Figs. 1 and 2], and [Plate 20, Fig. 2]).
The checkered pattern of the juvenile fades gradually as development proceeds. Persistence of the juvenal markings varies greatly in individuals and probably is subject to geographic variation also. By the time sexual maturity is attained the dorsal pattern often is indiscernible or represented only by faint traces. The ventral speckling is more persistent.
A female of 602 millimeters snout-vent length in mid-July 1962, at a probable age of 11 months, was described as follows: Overall dorsal color olive gray, but with remnants of juvenal pattern discernible; dark dorsal blotches have almost faded, but their edges, about one scale wide, are still distinct; low on sides, color fades to pale bluish gray, and to pale greenish blue on edges of ventrals; on anterior one-third of body midventral surface is lemon yellow; farther posteriorly it fades to ivory, almost white on tail; chin white, except for reddish brown posterior edges of last infralabials, and streak of same color on each antepenultimate infralabial; top of head olive gray with irregular scattered dark marks; preoculars pale centrally with olive brown edges; supralabials white with reddish brown triangular marks; postnasals white anteriorly, gray posteriorly; uppermost postocular brownish orange, paler centrally; two rows of semicircular spots on belly, distinct anteriorly, but fading posteriorly until indiscernible on posterior part of belly; numerous small black spots scattered irregularly over dorsal and lateral surfaces.
A male racer retained more of the juvenal pattern at an approximate age of 15 months, when he was described on November 30, 1961: Dorsal surface dark grayish brown, the large juvenal dorsal blotches (each about eight scales wide) easily discernible, but faint; top of head dark olive brown, mottled with black, paling in rostral region; supralabials white on their anterior and lower portions, marked with brown and blue-gray on their upper and posterior portions; chin white, but with rusty markings on last four infralabials; ventrals ivory-yellow with rusty spots of which the largest are approximately three-fourths of the ventrals' breadth; first row of scales bluish gray, or with greenish suffusion (in neck), most of scales having indistinct dark spots; second row of scales similarly colored but more suffused with dusky pigment, blending into the darker duller color of the dorsal surface.
A female of 720 millimeters snout-vent length, presumably about 20 months old, but not gravid, on June 13, 1962, was described as follows: Juvenal pattern no longer clearly discernible but scattered traces of it remain; dorsal color predominantly grayish olive, with occasional small black spots in streaks scattered irregularly over dorsal and lateral surfaces; at anterior end of body lateral scales have bluish green edges but this shading becomes less noticeable posteriorly; head mostly olive dorsally with marking obscure; parietals have a large faint blotch; supralabials retain faint dark, brownish markings on their upper parts; dark spot on median edge of each prefrontal; supraoculars slightly darker than adjacent scutes; chin mostly white, with yellowish suffusion at edges of scales; ventral surface predominantly yellow, but fading to grayish white posteriorly; remnants of juvenal ventral spots faintly discernible as tan or whitish areas on yellow ventrals.
Munro (1950b:124) mentioned a blue racer of 749 millimeters total length (hence probably having a snout-vent length of 600 millimeters, or a little less), which retained faint juvenal markings when caught on June 23, 1948, even though it was sexually mature, since it laid eggs on the night of July 4, 1948. During several weeks of captivity this snake's markings faded perceptibly.
In fully adult blue racers, those more than three years old, the juvenal markings have become completely obliterated. In those from the area of my study, the dorsal coloration is subject to much individual variation, typically olive brown, but ranging from pale bluish gray to dark brown, dark blue, or slaty. In most, the dorsal color is uniform, but in some there are streaks and isolated scales of black. The dark dorsal color extends down the sides onto the lateral corners of the ventrals and the subcaudals. The chin is white but the remainder of the ventral surface is ivory colored.
The slender and streamlined bodily proportions of the racer are subject to change through allometric growth. The head, and especially the eyes, are relatively large in the hatchling, and become relatively smaller as growth proceeds. The relative tail length seemingly increases in the growing young and then decreases slightly in adults.