User blog comment:SayuriDarling/The Mark of Athena Official Discussion/@comment-4388405-20121006181920/@comment-3146930-20121006212339

But the Eidolons don't simply leave the body when they aren't controlling someone. They just allow the person they are controlling to do whatever until they need to do something. When Piper told them to raise their hand, Leo raised his hand after saying it wouldn't work and then the Eidolons revealed themselves inside him, Percy, and Jason. Plus, they told the crew that Gaea had sent her three strongest after them. I don't see why they would control Jason, but leave Leo alone, who had spent the last six months working on the Argo II. Then wait another 6 months to control Percy. Heck, they should have taken control of him because then the ship would have been completed even later. Also, they always appear in threes and the only time Leo, Jason, and Percy were together was during this book.

As far as the glowing eyes, I don't see why Jason's eyes would be white. He wasn't blinded, he witnessed a gods magical divine form. When he looked at her, "Jason fell, light searing into his mind..." so when he opened his eyes, his eyes were filled with golden light.

As far as their eyes changing color, I just find it to be a creepy little undertone. The idea that the person you are looking at isn't the person that is standing there. Simply an identifying feature of the spirits, showing who is in control of the body.