Lots of what you have said is perfectly correct.

The only thing I would suggest is that to colour the lighter hair, you use these coloured hair 'chalks'.
I don't know much about them myself, but they come in every conceivable colour.
They eventually wash out but far less likely to stain the base and are probably kinder to the hair itself.

http://www.amazon.co.uk/Temporary-Pastel...B00AB0I4N4