Success!!
Thanks for all the advice on colours. It turns out, Mark, that I didn't need blue after all. A blob of white and a few drops of red makes a perfect match to the original. All hair are now (re-)coloured
Thanks for all the advice on colours. It turns out, Mark, that I didn't need blue after all. A blob of white and a few drops of red makes a perfect match to the original. All hair are now (re-)coloured