Really depends on how many applications you have put on to get it that colour. The colour will have to be taken out first and this may take a while or may lift straight out. Someone on here suggested washing it with head and shoulders to help strip the colour I usualy use washing up liquid that works as well. Also what looks nearly black to you may only be light brown to a hairdresser so best to pop into a salon and have them look. Or if you are near Worcester call me 077 29396684 good luck Regards Debra
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I would surgest you use standard head and shoulders and wash your hair lots as this will remove some of the colour from your hair, if it was a home colour it should wash out fairly easily. Where do you live ? It would help to see your hair as you may just need a bleash wash to strip the colour and then a full head of high/low lights to even out the colour. This would be about £80 for me to do but it depends on who does it and where. Do not attempt to put any more colour on yourself !
It will all come down to how much product the stylist has to use and how long it takes, You are probably looking at at LEAST £80.00 in most salons for it as it is a Colour correction. By that it means there would be several stages to colouring and correcting the Colour of your hair, and may take more then 1-2 stages to get it a Colour that you are happy with. Lifting tint out of hair isn't as easy as it may sound as you cannot lift tint with tint to the level that you may be wanting, so a stylist would have to use a Colour remover or a bleach. It would be advisable to have a test piece in a salon so that the stylist will know how long it is going to take and what will work best on your hair. They may then also be able to give you a better price estimate. You will probably find the process will take at least 2hours just for the colour alone, but depending on how much colour build up you have on your hair and your hairs condition, will depend on how easily your hair will lift up to a dark blonde colour without damaging the hair. Do not do it yourself at home, as many people make this mistake and it turns out worse then it was previously and may cost even more to correct it. I hope this information helps you!