For a second, I was half-convinced that their eyes were the same color as the snow surrounding them: pure, unbroken white that could've easily blinded anyone who stared too long. Then the boy (the older of the two, I guessed) tilted his head to look behind us and I noticed their true color.
My first guess wasn't too far off, honestly. Though their hair and skin coloration suggested that dark eyes were the norm in that family, at least at some point, theirs were of a blue so pale it easily reflected the sun banking off the snow they were sat in.
Later my mind suggested the word watchet to describe the boy's eyes; the girl's, though, reminded me more of the color of hyacinths in spring even with the slight glaze over them. Especially striking in combination with their pale, rosy skin and black hair that lay in unruly cowlicks even after being brushed; no wonder they'd been taken for experimentation. Anyone who looked even slightly outside the norm for the area was tracked down, hunted even, and these children definitely stood out.
So why had they been released, or had they escaped? Whichever it was, I wasn't getting anything out of them at the moment as they seemed to be mute. Also a misconception, I found...at least on part of the girl who almost never was quiet. By the time she'd been brought to a safer place, we all knew her name, age, and life story including the time they'd spent in the research facility. The boy -- her brother -- was less of the garrulous sort but gave in to his sister's cajoling when asked to sing to pass the time.