Written to: Safe and Sound - Capital Cities, crosspost from AO3
Glaucous: Frosted; pale-bluish grey, like morning fog.
Loki likes that he can tell Thor's mood just from the colour of his eyes, prides himself on his ability to read his husband like an open book.
Bright star-blue when he is amused, or when he is playing with Modi, or when he is training with the Warriors Three and Sif. Modi likes to imitate this colour for his own eyes, and this makes Thor laugh and pinch his cheeks and tell him what a good boy he is.
Thor's irises become shot through with green when he is confused (most often when he is reading a book, Loki has noticed, although to be fair, he was not aware that The Velveteen Rabbit was particularly mentally stimulating). Loki has also seen this confusion when Thor is faced with an instruction manual for one Midgardian device or another, and would it have helped to turn the manual right side up? It most certainly would have, but Loki didn't feel obliged to tell Thor that as he watched him struggle to put together a bookcase or a table or whatnot. He would often use Mjolnir to bang in dowels and nails, much to the warhammer's displeasure, and more often than not she would leave dents in the furniture's legs in her irritation. Thor preferred to ignore these.
His eyes darken when he is sad, or when it is raining. Despite being a god of thunder, Thor does not much care for rain, and when the skies open up above them, he pouts by the window as he stares out at the wet landscape. Loki likes to tease him, then, to put him in a good humour, but Thor shakes him away sometimes and insists on sitting by the window with a Nicholas Sparks novel and a cup of tea. Loki adores the rain, but not so much the Nicholas Sparks novels.
But Loki's favourite colour is probably the grey-blue slate of Thor's eyes when he just wakes up, before he fully processes that it is another day. Loki sometimes wakes up before Thor just to watch him wake up, too; he watches from under lowered lashes as Thor's eyes open, blinking away sleep, bites the inside of his cheek to stifle a laugh as Thor's eyes alight upon his face and those lovely grey-blue eyes crinkle at the edges as he smiles.