Here's a couple of charts for the stages hair goes through while lightening as well as how to colour-correct and tone hair.
Stages While Bleaching. NEVER bleach to white. It's not on the chart for a reason--your hair will go there, but it will be completely fried when it reaches that level.
Colour Correction Chart (toning). You want a diluted version of the corrective colour. It goes both ways, as well--if your hair is too ashy and you want to warm it up, add a bit of yellow.