As so far ther's been only answers for dark reds I'll put in my advise for really bright strawberry blond hair. For that purpose I use a bright orange as a base colour and highlight/drybrush it the same way as blonde hair, with a mix of GW Iyanden darksun and white. The result will be more a sort of reddish blond than truly red, but then again that's what most real red hair look like.