The female Green-veined White butterfly has a black/grey corner and two spots (and usually a grey streak) on each forewing. The corner is less dominant than on the Large White.
On an indistinct corner, it can appear as three black spots, one of which is on the corner mark.
The male Green-veined White butterfly has less distinct markings and only one spot on each forewing.
The early generation has greeny-grey shading along veins on the underside of its yellowish hind wing.
The later generation has more pronounced grey shading on the underside of the hind wing.