Diaphanous: adjective
1) of such fine texture as to allow light to pass through; translucent or transparent.
2) vague or insubstantial
His skin is almost translucent in the sun.
You admire the play of the sunlight across his hipbones, the dark shadows the jutting bones cast on his hard abdomen. You watch the shapes spread across his abs as the tree outside the window waves its leaves, and you watch on the screen of his chest as one leaf detaches itself from the tree and spirals gently downwards. Your gaze follows the path of the leaf, tracing the patterns of his muscles before becoming distracted by the light that streaks along his prominent collar-bones and pools into darkness.
His shoulders are broad and smooth, the skin pale and stretched tightly across muscle and bone, and your eyes run almost deliriously down his strong arms to the delicate formation of his wrists. One hand is flung to the side and the sun has chosen this hand to shine on, this hand to favour with its beam of light. You can almost see through his skin, the fine bones just rising up to create thin ridges and shallow dips and the shadows are beautiful. You've never been a particularly creative person but in that moment, you know.
Sirius Black is a work of art.