Without seeing your colour it’s difficult to advise you specifically and if in doubt, you should always take the advice of a professionally qualified colourist… However, I can say that the unwanted green tone that you mention is generally associated with chemicals know as metallic salts. These are a bit ‘old-skool’ now in terms of colouring and don’t often appear in professional products if at all. However, some of the older, cheaper home hair dyes (depending on the source and country of origin) may contain chemistry that would create incompatibilities with professional hair products.

It’s not a problem if you visit a good colourist who will offer to do a ‘strand test’ on your hair to check the chemical compatibility… This usually involves cutting a few strands of your hair and taking them to one side for analysis. If they really know what they are doing, they will cut a few strands from one or two or your highlights and lowlights as well as from your natural hair. You can usually have the results the same day or within a couple of days.

Assuming that your hair isn’t going to react in the way I have just described and turn green, the more likely mistake if any would be that your hair could appear slightly mauve or violet in certain lights, as the blue/purple end of the spectrum are the colours that give us ash toning. Yellow and blue are opposites on the colour wheel, so we use blues and mauves to counter golden and copper tones in blond hair.

The chances of your hair turning blue are highly unlikely unless your hair is very dry and a particularly aggressive toner is used. A decent colourist will be able to advise on that too.

The Advice? Well, if a colourist thinks you might go green, get a strand test done (they shouldn’t charge you if you are planning to have a colour service with them.) If the strand test comes out well and you are confident in the salon, go for it! If you are worried about going a bit blue, remember that toning is something that can be built up gradually. If you share your concerns with your colourist, they should be able to add a smaller amount of ash to the mix and perhaps cool your colour tone further over two or three sessions.