If you have any hair colour on your hair whether it is semi-permanent or permanent, then it can and will affect any other colour you put on your hair.
One important rule to remember is that TINT WON'T LIFT TINT, therefore if you want to go lighter and have a colour on your hair already, then you can't do this with a normal hair colour/dye. The main thing you can do is to use bleach, either in its full strength form or in a weaker form like a bleach bath
(this can be done at most hair salons) or there are other specialist products out there which remove colour from your hair, like the Affinage Eraser available from our online shop. Visit our 'Hair Colour Removal' Page Here for more information on this professional hair colour stripping product.
Once the previous colour has been removed out of the hair either with the bleach or colour remover, you would then apply your target colour.
Remember that bleach isn't a colour, it is a product which removes colour out of the hair so you would usually need to tone the hair afterwards.
If your hair has been coloured very dark previously and you want to go much lighter then this would take a few applications of the bleach or colour remover. This would need to be done over time and not all at once, as too much bleach on the hair over a short period of time can cause damage and dryness.
If you do go to the salon to have colour lifted out of your hair, always ask for an estimated price as these hair processes can be very costly due to the amount of time they take, and the fact that you may need to go back every couple of weeks to get more colour lifted out of your hair.
If the previous colour on your hair is red and you want to change to a completely different colour then this can sometimes be quite tricky. Although reds are the colours which tend to fade quickly out of your hair, there is usually always some red left in there and this bit of red is usually hard to shift.
The more intense the red, the harder to remove from the hair.
If the red is quite a bright intense red and you eventually want to go lighter without the red, what you can do in the meantime is use an ash brown colour to cancel some of the red out.
Keep doing this over a few months until some of the intense red under the brown has subsided then start to think about going lighter.
If you attempt to remove the red with bleach then what you tend to find is that bright deep reds can go pink, purple reds can go lighter red and copper reds can go quite golden.
The science behind colour:
When hair is lifted with bleach, the colour molecules are removed in a particular order due to the size of these molecules. The black and brown colour molecules are removed first and very quickly as they are large and easily come out of the hair, then the red and yellow molecules are removed last, but due to these being a lot smaller, they take longer to lift out of the hair.
So the order hair is lifted is: from black to brown to red then yellow.
This is why when going lighter such as going from dark to blonde the hair can sometimes get stuck in the red-yellow stage of colour removal, and can leave the hair in the orange stage. The stage after the orange is removed is yellow and then after that, all colour is lifted out of hair so it looks almost white.
That is when the lifting process is finished.