#iirc there was a point in my fanfics wherein I tried to distinguish between Espio's and Silver's eye colours

[true-blue-sonic]

It's interesting to me that Silver is associated with the Chaotix because they all have amber eyes

Haha, indeed! Luckily not all exactly the same shade; Espio's are more yellow-golden, Vector's are described as 'goldenrod' on the wiki, and Charmy's are more orange. I tried to compare Espio's and Silver's models on the wiki, and it seems like Espio's eyes are a *little* bit more golden whereas Silver's are more yellow? But their fur/skin hues and eye colouration differs between slightly each game, so I don't think any solid conclusions can be drawn from that. As it stands, I don't think there is any deep meaning behind it, what with the Chaotix getting their modern redesign three years before Sonic '06 was released and Espio and Silver only teaming up a year after that. But I think all four of them look great with their specific eye colours!