Hello Silviya,
Firstly, the main reason there is a line between the colours is because the brushing technique used to blend the applications of colour wasn’t feathered enough. This is what ensures the blend is soft and seamless between different shades, creating that sun-kissed look rather than dip-dye.
In these instances, if you have been to a salon, go back to them and they will always be happy to take a look at the colour again for you. Home-colouring to rectify unsatisfactory colour often complicates it further and can cause colour build-up, unevenness or banding. Possibly the colour you chose wasn’t quite dark enough to disguise the line fully. In this case, it could be resolved by booking in with a professional colourist who can work through the hair section by section, using freehand balayage techniques to break up any remaining line with lighter, sun-kissed tones. It may not result in exactly the colour you had initially wanted but will be very close and more natural looking.
Linzi King, SWH Team Specialist, Simon Webster Hair, Brighton