This species is a typical member of the genus. Both genders typically have pale yellow wings above with no traces of orange, unlike its close cousin the orange sulphur which may also be yellowish. Males have clean borders, while females have yellow dots within this region. Females sometimes exhibit a white form known as alba.
The underside of the male’s wings is yellow while the female’s is yellow or greenish white, and both have a doubled hindwing spot trimmed in brownish red. The hindwings show a series of four small red spots along the outer third portion, a trait that distinguishes the other North American species such as Colias interior, except for the orange sulphur which also shows them. Its wingspan is 32 to 54 mm.
This species has white form alba which can be very common in some populations, while rare in others. It can be confused with other white forms of Colias, particularly that of Colias eurytheme. It can often be distinguished by the border pattern of both wings, though some individuals are impossible to separate without the presence of other “normal” specimens. Though they differ in flight style, the white forms of Colias may be confused with other pierids such as Pieris rapae and Pontia protodice. White-form males are also known, but exceedingly rare in this species.
Under The White Oak Leaves 