Working on a drawing of River and the Doct...well, no, not the Doctor exactly...hence River's somewhat apprehensive expression. Spoilers.
This is a scene from my fic Doctor Who: Civil War (sequel to The Lemkin Factor).
They are covered in glow because the caves of Gemina are covered in luminescent moss and fungi that easily comes off on the skin.
PS- I'm dreading having to try to draw all of River's amazing curly hair.