[Kurona]

Quote:

Originally Posted by weedle013ZiO

W can be accounted for as the Cyclone and Joker colors. For #1, I don’t know.

Then just to add the other examples we know of; Faiz, Den-O and Fourze have yellow, red and orange eyes respectively but the colour of the animal on their stamps are red, white and blue. Den-O and Fourze already use red and orange for the back of their stamps, but they could have easily used white instead. And then you've got Zi-O, who has the strange choice of a yellow animal on a pink background.

Eye colours will usually be used for the Vistamps, but that's not a pattern in and of itself; it's because usually they're one of the most notable colours in a Rider's scheme. Keep in mind as well they also likely want to diversify how these stamps look by colour so they don't look like one another.