Can you mix hair dyes?

[LaurieFairyCake]

I don't have 2 packs the same and I'm not particularly keen on either colour

And I need to dye every 2/3 weeks because of Grey coming through ..

Personally I wouldn't because you don't know how they'll react together. Mixing chemicals will never end well.

It's ok, as long as you keep the ratios. I've done it loads of times, it's fine