The color pattern changes in the course of development, and the shade of
color changes in response to environmental conditions. At the time of
metamorphosis, young are dark brown with specks of black and with a
dark, cuneate, leaflike middorsal mark. The narrow end of this mark
arises just behind the head, and the mark extends posteriorly as far as
the hind leg insertions. At its widest, the mark covers about half the
width of the dorsal surface. The lateral edges of the mark are sharply
defined, but at its anterior and posterior ends it blends into the
ground color. In most individuals smaller than 20 mm., this dorsal mark
is well defined and conspicuous. As growth proceeds, however, it becomes
faint. In frogs 19 to 25 mm. long the marks have disappeared. In
individuals of this size the brown ground color is markedly paler than
in those newly metamorphosed, but is darker than in adults.
In large adults the dorsal coloration is a uniform pale tan, paler on
the average in females than in males. Temperature and moisture both
affect the shade of coloration. In frogs that were partly desiccated,
the color was unusually pale, with a distinctly greenish tint, and at
high temperatures coloration tended to be relatively pale.
Hecht and Matalas (1946) have described and figured color patterns in
various populations of _Gastrophryne_, demonstrating geographic trends
and helping to clarify relationships. Their account indicates that the
dark dorsal mark present in young of _olivacea_ but not present in
adults, is better developed and longer persisting in other forms.
Specimens of _carolinensis_, presumably adult, are figured which have
the dark middorsal area contrasting with paler color of the sides. The
dark area is seen to consist of dots or blotches of black pigment which
may be in contact producing more or less continuous black areas, or may
be separate and distinct producing a spotted pattern. Pigmentation is
usually most intense along the lateral edges of the dorsal leaflike
mark; the central portion may be so much paler that the effect is that
of a pair of dorsolateral stripes. This latter type of pattern is best
developed in the population of Key West, Florida. Hecht and Matalas did
not consider these insular frogs to be taxonomically distinct, because
only 48 percent of specimens from the Florida keys had the "Key West"
pattern, while 29 per cent resembled _olivacea_ and 23 per cent
resembled _carolinensis_. In the southwestern subspecies (or species)
_mazatlanensis_, recorded from several localities in Sonora and from
extreme southern Arizona, the dorsal pigmentation similarly tends to be
concentrated in dorsolateral bands, but is much reduced or almost
absent, and there is corresponding pigmentation dorsally across the
middle of the thigh, across the middle of the shank, and on the foot.
When the leg is folded, these three dark areas are brought in contact
with each other and with the dorsolateral body mark, if it is present,
to form a continuous dark area, in a characteristic "ruptive" pattern.
Hecht and Matalas found similar leg bars, less well developed, in
certain specimens of _olivacea_ including one from Gage County,
Nebraska, at the northern end of the known geographic range.