He never noticed it.
Never noticed the blanketing of deep blue, no longer merely the effect of the soft glow of the arc reactor, sweeping over the other man’s skin, leaving still darker lines of cobalt across the smooth planes of skin.
Never noticed the slow, creeping chill that seeped into his flesh wherever their bodies touched, which left his thighs numb and tingling where slender fingers dug into his muscles.
Nor, had the thin blue lids fluttered open, would he have noticed the shifting of sea-green eyes to a dark red colour. All of the monumental focus, all the rapidly firing neurons in Tony Stark’s brain were zeroed in on the press of the other man’s lean torso against his abdomen, on the slow scrape of teeth against his throat, and the way that the Asgardian’s cool lips brushed the rhythmic pulse of his jugular.
An unexpected clamping down of teeth set a low noise rippling through his throat and the other’s eyes opened briefly, one hand sliding up Tony’s side with excruciating slowness, tapered fingertips leaving a trail of frozen prints along his ribs before slipping up to his bicep, where they curled over the muscle in what could have almost been a caress, were it not for the firmness of the long fingers gripping onto his arm.
Forcing Tony’s head back further against the cushion made from the crook of his arm, Loki’s teeth grazed and pressed against the other man’s adam’s apple, his entire body shifting upwards, sliding chilled skin over warm and ripping a ragged gasp from his throat. Oblivious to, or unheeding of the cold of the other’s body, Tony’s back arched, bringing his own body to bear against the seeming delicacy of the other man’s form.
As if in response, the Asgardian’s head tilted up, catching the other’s earlobe in his teeth, his narrow hips arching fluidly against the other man’s in a movement that seemed to travel through his entire body and ended with a near-silent puff of air slipping past his lips. It was to that puff of air, that nigh-inaudible sigh, that Tony was lost entirely.
And still he never noticed.
It wasn’t even until five minutes after he had climaxed, gasping and drenched in cold sweat, that Tony lowered his head and looked at the man draped over his chest, but by that point it no longer mattered. The skin was pale once more, though still cool to the touch, and the eyes that raised themselves ever so slightly, were the same green that they had been when the evening had begun.
But for days afterwards, Tony tried to figure out the origin of the raw, sore marks that littered his body - marks JARVIS identified as appearing to be frostbite.