紫

How it works

This is a little recipe sentence. と (and / with) joins 赤(あか) (red) to the next item, and を (object) marks 青(あお) (blue) as what gets acted on. The second と (when / if) is different — attached to the verb 混ぜる(まぜる) (mix) it means “when you do this, that happens”. Finally に (into) plus なる (become) says the result turns into 紫(むらさき) (purple).