So imagine this:
Alec likes to sketch. It's his form of relaxing. After he met Magnus he has started to draw him everyday with different techniques.
Sometimes just pencils, sometimes charochal or markers. He loves to do that. And right after he learned about Magnus' true eyes he really wanted to draw them. So he has started to try. But, surprisingly he never could got them right. Like ever. Something always seemed to be a bit off to him.
So he has started to gently persuade Magnus to let the glamour down when they are alone just to mesmerise to beauty of them. Slowly, really slowly, Magnus started to do so.
On one of particularly peaceful evenings Magnus caught Alec staring at his eyes and asked him what he was looking for in them. Alec only smiled but Magnus asked him again making those puppy eyes that he knew Alec could not resist. So Alec blabbed and told him about the drawings. Magnus wanted to see the sketchbook ASAP and Alec, with a deep sigh, brought it to him.
While Magnus was in awe, looking through the sketchbook, stunned by Alec's skills, the shadowhunter looked at him and finally it striked him. He know what was missing in his drawings. The pure spark that Magnus has in his eyes that made them feel so alive. Plus he noticed that depending on the angle that light were hitting the eyes, it's colour were slightly changing.
He smiled to himself and brang Magnus close to him, ruffing his nose in the other man's hair and lightly smiled.
"I love you so much" he whispered.
