This is something I'm still sussing out for the new WIP, The Goddess of Vengeance.
My MC, Lauren, is a bi-racial girl (African-American and Caucasian) with medium-brown skin and warm brown eyes with golden flecks.
My problem with eyes at present? She's possessed by the Greco-Roman Goddess of Vengeance, Nemeses. I can't picture the goddess of vengeance with warm brown eyes. I've been thinking that one of the changes that the Goddess works on the body she possesses is to slowly change their eye color to her own. When Lauren next meets up with Willow, whom Nemeses inhabited until she was passed to Lauren, she'll notice that Willow has very pale blue eyes, with the color almost leached out. Can't you picture cold, pale blue eyes staring out of the dispassionate face of the Goddess of Vengeance?
But, I don't want to be eye-color-centric. I'm a blue-eyed girl myself. My MC in Shards, April, is a blue-eyed girl too. I promise, I'm not blue-eye obsessed. I just want to do what feels right with my story, and this obvious evidence of transformation for the possessed body feels right to me.
Since Lauren fights to temper the goddess' urge to vengance, I was thinking maybe her eyes will never turn cold, but the process will change her in a visible way. Maybe her eyes will slowly turn hazel, and then green, as she fears turning into Willow. And then eventually, as her eyes stay green, she'll realize she's successful in fighting the Goddess and doing her bidding simultaneously -- bringing something like justice to the opressed, rather than vengeance.
Not my most informative post ever, but I'm just musing here about what will work in the WIP.