it isn't the first time Ikeda has drawn Tsukune with different eyes. Just the first time he has coloured it.
I think it is to represent the two halves of his "soul" so to speak
bought Volume 5 today (and Cross Game 4
) it finally came into my local store.
colour page is a mini poster of Moka and the Watermelon Jack o Lantern
Omake is about San's time at Youkai (with Gin and Karate lolicon)