I only have one observation on the paper: it would be interesting to study the interplay between contrast and aspects of a face's geometry. Generally speaking there is sex dimorphism in lip geometry, with women having fuller lips. Lips that are too narrow or too full, however, are rated less attractive. By applying a dark shade on very narrow or very full lips, one may be emphasizing this unattractive trait and thus reducing the overall attractiveness of the face. It would be interesting to see whether increased contrast has positive effects across different facial geometries.
Another possible interplay might be between facial symmetry and contrast: enhanced contrast in an asymmetric face may bring into attention this asymmetry in a more pronounced way.
Finally it may be interesting to study the interplay of contrast with pigmentation traits: how does tracing the outline of the eyes affect attractiveness for light vs. dark eyes? How does pigmentation of the hair (which acts, as I have argued before, as a "frame" to the face, contrasting with lightness of skin), or conversely skin tanning combined with light hair, interplay with facial features?
Perception 2009 volume 38(8) pages 1211 – 1219doi:10.1068/p6331
A sex difference in facial contrast and its exaggeration by cosmetics
Abstract. This study demonstrates the existence of a sex difference in facial contrast. By measuring carefully controlled photographic images, female faces were shown to have greater luminance contrast between the eyes, lips, and the surrounding skin than did male faces. This sex difference in facial contrast was found to influence the perception of facial gender. An androgynous face can be made to appear female by increasing the facial contrast, or to appear male by decreasing the facial contrast. Application of cosmetics was found to consistently increase facial contrast. Female faces wearing cosmetics had greater facial contrast than the same faces not wearing cosmetics. Female facial beauty is known to be closely linked to sex differences, with femininity considered attractive. These results suggest that cosmetics may function in part by exaggerating a sexually dimorphic attribute—facial contrast—to make the face appear more feminine and hence attractive.