So, all the other girls including Yuki have red bows, however when inverted. You get the same color as Kei and Miki's bows. : r/GakkouGurashi
Someone mentioned Yuki's uniform being a different color. I'd like to point out that in this scene all the girls around her, their uniforms changed to green when they turned into zombies. :
School-Live! Gakko Gurashi! Living at School! Kurumi Ebisuzawa School Uniform Cosplay Costume
4557487 school uniform, Sakura Megumi, Naoki Miki, Wakasa Yuuri, Ebisuzawa Kurumi, Takeya Yuki, Gakkou Gurashi! - Rare Gallery HD Wallpapers