Hmm! I'm.... actually kinda pondering whether or not this would be foreshadowing! Like... is there a reason to believe that's weird, within the story, or are we supposed to suspect that green hair is normal but purple-ringed eyes aren't? Is there an indication anywhere that eye colour is important?
To me, those sorts of things are where foreshadowing comes in. Someone mentions that eye colour is important, or to look out for strange-coloured eyes, and THEN we'd notice "huhhhhhhhh what's up with Jack's eyes then,,,,," Or someone asks Jack what's up with his eyes, and THEN we start really noticing any unrelated information about eye colour that gets mentioned elsewhere. Your comic has a lot of really distinctive, colourful designs, and there's a lot that we quickly adjust to as being normal -- so to introduce this guy and just let us take in his design only tells us "this is a colour of eye that exists in this world."
Which is probably why nobody has commented on it, I'd guess!
I definitely put it in on purpose. My comic has, uh, a lot going on, so if I don't sit down and figure out "okay here are the things I need to foreshadow/set up/hint at and we need to see that by X point in the story" then I would end up forgetting to mention important details until right before the relevant scene.
I scribbled this a while back to show a friend how I tend to conceptualise this stuff with my comic:

Both of these are establishing/setup things, but it's the same basic idea -- I know where the payoff is gonna be, so I look at the rest of the outline to figure out when would be a good scene to drop a little hint about something. I make the same notes about character dynamics, too -- I've gone so far as to write down every scene that particular characters were in, in order to figure out how they should be coming across in each scene and when I should start dropping hints of upcoming shifts so that they don't come out of the blue.
That's maybe more writing out stuff than is strictly Necessary but it's the only way I can hold all this stuff in my brain!!