Rainbow-coloured hair is a commitment. We're not talking tattoo level — more of the sublet-housemate variety — but a commitment nonetheless. You and that unicorn hair are going to be together for a while — from its unveiling glory until it fades and your roots grow in.Don't get the wrong idea: We're not here to deter you from diving into fantastical colour . We're just going to lay down some groundwork for what you need to do if you want to swap one bright colour for another — or if you want to go back to your roots.Ahead, two of NYC's top colourists give us 10 rules by which to live and dye:Celebrity colourist, and the woman behind some of Instagram’s coolest colours, Aura Friedman says you have to let that colour fade. The longer you let it be, the better for your hair health and the better results you will get with your next colour. “Blue, green, and purple can be stubborn,” she warns.If you must change the colour right away, colour genius Roxie Darling , of NYC’s Hairstory Studio , says it's best not to do anything too extreme. “Try to ‘brown out’ the vibrant colour that you already have by adding brown to the bright colour,” she says. “You might still see some of the original colour underneath, but it would help to do that instead of trying to strip out the vibrant colour and damaging your hair further with bleach.”“If you are going from any bright colour to brown, you can generally just put a shade of brown over the bright,” says Friedman. “However, if you don't want the colour to peek under the brown, then you must neutralise the bright colour. For example, if the bright colour is red you must use a green-toned brown to neutralise the red. And if you want to be blond, you must make sure that your hair is healthy enough to remove the colour. The last resort should be bleaching.”If you are going from one bright colour to another, it is best to stay within the same colour family. “Usually, if the colours are in the same family it’s not that hard to go from one to the other,” says Darling. “For example, if you stay in the warm tonal family it’s easier than switching from warm to cool. Switching between warm and cool families is what will make it more difficult and can cause the colour to get muddy.”When it comes to changing your hair colour, there is not an exact formula. It all depends on your natural hair colour, the colour you dyed it, and the colour you want in the end. There are so many possibilities. “Everything depends on your natural colour and the saturation of the colour that you’re trying to remove,” says Darling. “In order to create brown, you have to mix opposite and complementary colours and you have to be willing to possibly go through some awkward phases — unless you have a really good colourist.”Yeah, you can do it yourself. But to really ensure you don’t end up with a muddy mess, it’s best to leave the job in the hands of a pro. “I will always recommend seeking out professional help for hair adventures like this,” says Darling. There is really no way to 100% ensure your hair won’t turn out muddy or a weird colour even in the salon, but a good colourist will stack the odds against it."It helps to be consistent with who you see because they will have a record of everything they’ve put in your hair previously," says Darling. "When I take people back and forth, I really rely on that record. It’s a bit like a health history; you have the ingredient list of everything that’s ever entered or left the hair, which is really useful when making decisions on where to go next."Darling recommends taking care of your post-rainbow hair the way you would when it was multicoloured. “You have to remember that underneath all of this your hair is still bleached and is delicate,” she says. “So I would recommend washing every two to three days with Hairstory’s New Wash , which also will help maintain your new colour so you don’t revert back to the vibrant colour. If your hair is feeling extra dry, you can let it sit for 10 minutes once a week as a deep treatment.” Friedman says to make sure that your colourist includes bond-builders like Brazilian Bond Builders with any dyeing you do to keep your hair strong throughout the process.“Make sure [getting rainbow hair] is a decision that you’re ready to make,” says Darling. “I just went from unnatural back to natural — and now I’ve returned to unnatural — and it’s definitely a decision that should involve a lot of consideration.”“Be open to different results and ideas," says Friedman. “You can't get stuck on one thing and be too controlling or exact with where you want to go next [with your colour]. And always keep in mind that the integrity of your hair is the most important.”