tips for colorful dyed hair?

So I got my hair professionally dyed blue (and spent way too much but it looked amazing) the dye they used was amazing and lasted 4 months without really fading much, anyway I got bored with the blue so I had my friend (bad idea x.x she messed up the bleaching) and my mom (saved my ass) help me dye it pink/purple. I wanna know what tips you'd think would help to keep the color for as long as possible. I already know the basic cold water and not washing it every day.