This is a character contrast trope. Both female characters are decidedly feminine but in different ways. The light is generally angelic and feels love, whereas the dark is generally devilish and plays with desire. The light is usually sweet and naïve, whereas the dark is usually aloof and brooding. Either type applies to a Tomboy and Girly Girl contrast. May overlap with Hair-Contrast Duo when their hair color is used to denote their light-and-dark femininity. When a love interest is involved, it's likely to lead to a Betty and Veronica love triangle: Betty being the Light Feminine, and Veronica being the Dark Feminine.