Tom and Maile's "lipstick" palms, redly wet in a light rain. I've done a few HDI images like this, for example the lychee tree from November 20th . The technique is hardly a secret, and it's very simple, provided you have a tool that allows saturation changes by color. All I did here was to desaturate green, which (as is obvious) turned green leaves into gray leaves, while leaving the other colors alone. It worked because there was almost nothing but red and green.