Oh god help, I couldn't stop laughing for 2 minutes:
Bit of a misinformation though, as Yukari's eyes aren't actually blue, and Yuuka isn't Red. If you combine Yellow and Green together though, it's like the spectrum of yellow and green scattered all over and became Red and Blue; just think, Green = Blue + Yellow, but this impurity of Green made it turn Blue, while this impurity of Yellow dragged pushed the other pure Yellow farther and eventually got it to Red. Think of it as playing with the color wheel. Oh my, I must've thought too much.
Bit of a misinformation though, as Yukari's eyes aren't actually blue, and Yuuka isn't Red. If you combine Yellow and Green together though, it's like the spectrum of yellow and green scattered all over and became Red and Blue; just think, Green = Blue + Yellow, but this impurity of Green made it turn Blue, while this impurity of Yellow dragged pushed the other pure Yellow farther and eventually got it to Red. Think of it as playing with the color wheel. Oh my, I must've thought too much.