red bush tea

Can't help you there as I spray it on virgin red-brown roots, I heard that it could discolour bright hair but am not sure if the stain could be successfully washed out...

I used to spray it on my bleached platinum hair and saw no staining from it so it shouldn't be a problem.
I need to get back to spraying my hair now I chopped it all off, I'm gonna need all the help I can get.

Would it make any difference to spray twice a day instead of once a day?

You can spray as much as you like, I used to spray loads in the summer as a way of cooling off my head. It depends on how your scalp reacts to it. Sometimes when I made my tea too strong it would make my scalp greasy so I couldn't have done it many times a day.