In the Illusion of Sex, two faces are perceived as male and female. However, both faces are actually versions of the same androgynous face. One face was created by increasing the contrast of the androgynous face, while the other face was created by decreasing the contrast. The face with more contrast is perceived as female, while the face with less contrast is perceived as male. The Illusion of Sex demonstrates that contrast is an important cue for perceiving the sex of a face, with greater contrast appearing feminine, and lesser contrast appearing masculine.
Russell, R. (2009) A sex difference in facial pigmentation and its exaggeration by cosmetics. Perception, (38)1211-1219.illusioncontest.neuralcorrelate.com
"The physical anthropology community has shown that male skin is darker than female skin (e.g. the work of Peter Frost). I have shown that while male skin is darker than female skin, male eyes and lips are not much darker than female eyes and lips. The result is greater contrast in female faces between the eyes, mouth and the rest of the face. People use this sex difference in facial contrast to decide the sex of a face and how masculine or feminine it is. Manipulating this facial contrast has opposite effects on male and female attractiveness. Interestingly, cosmetics exaggerate this sex difference, which suggests that cosmetics are used to manipulate sex differences to make the female face more feminine, and hence attractive."