Rosy cheeks seem to be crucial in the dating game, for monkeys at least.
Females of a common primate, the rhesus macaque, prefer males with red faces, a study has shown.
It signals high levels of testosterone which, in many male animals, mean a healthy immune system and good genes.
Females preferred the face on the right
A rosy glow might also act as a similar cue in humans, say British researchers. They speculate that it could explain why women use rouge and lipstick.
"Non-human primates have the brightest colouration among mammals in the animal kingdom," says Corri Waitt, a researcher in the department of psychology at Stirling University.
"Nobody really knows why - but it could play a role in competition with other males or female mate choice.
"We have found that the females do seem to be interested in the bright colouration."
The theory that female primates are attracted by male colouration is, in itself, nothing new - it was first postulated by the great naturalist Charles Darwin in 1876.
But this is the first experimental evidence in support of the idea in non-human primates, say the British researchers.
The team used a computer to manipulate images of 24 wild adult male rhesus macaques.
They tested pale and red versions of the faces on six female macaques kept in captivity and measured their response.
The females spent much longer looking at the red faces and used gestures such as lip-smacking to show their interest.
Craig Roberts, a biologist at the University of Newcastle, says it raises the possibility that cues in facial appearance may play a similar role in humans.
"The trick for the female is to pick the male with good quality genes," he says.
"The difficulty is in what physical trait displays that underlying genetic quality.
"It seems that red colouration - which is difficult to maintain in poor health - gives an honest reflection of the male's underlying genes and healthiness."
The research is published in Biology Letters, a journal of the Royal Society
Rhesus macaque image courtesy of the University of Stirling/Royal Society.