One of my favorite Sonic designs 👍👍👍

Earlier version of him without the Pac-man pupils.

One of the biggest references I used for him was this one image of Felix the Cat that looks really uncanny valley looking and odd.

Re-releases after 1993 kept his grey eyes in-game. Though D.A. Garden (2011) sprites dipict him with red.

I think this is less an error and more a case of Metal's sprites being made when his design concept was being finalized.