Whoever is responsible for colouring the credits page forgot that they're... somehow... identical quins. Unless at least 4 of them are using flashy hair-dye (which I don't believe is permitted in Japanese schools), it is impossible for them to have such different hair colour.
Also Itsuki's idea of manliness is just fine. Most of the people I used to hang out with dressed like that.
I sometimes dress a bit like that but I'm usually more toned down (plus I prefer long-coats).