Yep, green is the rarest eye color, Google confirmed it. Also this goes for Amy, Rouge (Well blue green), and a few other characters. Its only three characters I could list, I cant list any other characters with eyes that have a greenish tint.
They changed the character design with Sonic Adventure to modernise it for the times, but it didn't have a plot reason. It's the same reason his voice has changed between titles, because they hired different voice actors, but there's no real plot reason for it because it's not something that happened in. What is up with Sonic's eyes? Sonic's eyes are a complicated issue, especially as the character has transitioned from 2-D to 3-D and been redesigned over the years.
As of now, Sonic's two eyes combined to form a single larger eye with two pupils, and his widow's peak descends very far down, almost to his nose. This is an important milestone as it marks Sonic's in-comic transformation from the old Genesis look to Mr. Green Eyes.
Wanna know why his eyes changed color? I've noticed that some people have trouble getting colors of the characters right (especially those with various vision problems), so I thought I'll help by giving you some color values. The color blue was chosen to match Sega's logo. In his initial concept art and first video game appearances, Sonic had black eyes with visible irises.
His spikes were short and his body proportions were rotund. As the Sonic series evolved, Sonic adopted the taller and slimmer physique he is now known for, along with his trademark green eyes. After all, you're trying to make a believable explanation for a blue hedgehog that runs fast and eats chili dogs.
Therefore, for the sake of simplicity, Sonic is a cartoon character, cry about it. Another crucial point to acknowledge is that Sonic doesn't have a single eye; he has two eyes. I doubt any of Sonic's thoughts would change his eye color.
If you really want some sort of theory though, maybe hedgehogs just have those kind of genetics. Reply reply Demetri124 Well looking at real hedgehogs their fur stops around their mouths and eyes, their eyelids are usually the same color as their snouts Reply reply thehypotheticalnerd.