Hanzo:
The first time he saw the miracle in his S/O eyes, he thought it was a result of being injured during the previous mission. He rushed to their side, fear on his face. "Is everything ok Hanzo?" They would ask as he looks in their eyes, confused by how they were not hurting. "Your eyes, they are 2 different colors, is this some kind of magic I do not know about?" He questions as they would shake their heads. "it's not magic...I was born with these 2 different colors for my eyes." They would say with some fear and sadness in their voice. "My Love, I am not saying that it is a bad thing. I was stating that I have never had a chance to see how beautiful the colors are in your eyes. On anyone else, they would not be as beautiful but for you, they make the whole soul I fell in love with even more precious." He would finish with a kiss and a smile. Yep, he is pay closer attention to them.
Genji:
He would first notice their eye colors when they come to help him calm down one night after a rough mission. He was tired but he could not fall asleep so he tried to meditate outside under the moon. As he started to relax, he hears someone behind him and he grabs his sacred blade, ready to defend himself. As he goes to attack, he comes face to face with his beloved. "S/O-san, what are you doing up? You should be resting." He would ask as they come to sit by him. "McCree told me that it was a rough fight...Genji, please look at me." They would calmly ask as he looks at them, noticing for the first time that their eyes are 2 different colors but just by looking in their eyes, he felt relaxed. "Shall we meditate together then retire to bed." They offer as he nods and takes a deep breath, allowing his eyes to close. Let's just say, now when he meditates, he thinks about the marvelous and beautiful colors that are in their eyes.
Sombra:
If she looked up from her computer for longer than 5 seconds, she would have seen that they had 2 different colored irises but it was only when her S/O was having a hard time looking for their contacts that she realized it. "Why are you wearing 2 different colored contacts?" She asked after a moment of thinking. "Dear, I have always had 2 different colored irises...I have Heterochromia, I was born with it." They would reply as Sombra would smile at them and grab their hand. "Wear your glasses more often, I like how they look and I don't think they are doing you justice." She winks at them as they blush. For now on, contacts are for battle only.
Tracer:
Most of the time, she would have her goggles on so the world could be slightly discolored and she sees that golden color that comes from her protective goggles. She would notice their eyes the first time she took off the goggles for cleaning. She saw the mixture of the colors and fell in love with the beautiful detailing and amazingly contrasting both irises are. "Darling, I love the color of your eyes, they look smashing on you." She would say with a wink, making them blush. Let's just say that she would keep looking in your eyes for now on just to see the beauty of the world because even something that most see as a weird mutation, she sees as a unique gift her S/O possess.