Blonde on Blonde is better done on a darker natural base color to achieve blended levels of blonde. Sofia Vergara , Madonna, J-Lo who are natural level 4 dark brown hair color have to “bust the base” meaning you have to lift the natural hair a few levels with just hair color. Then go in and foil work the rest with highlights. This gives the hair a natural looking blend of color that will match the skin tone of that individual. Lighter natural hair color can be blonde on blonde also, but for a natural dark color its more natural to lift the base first. To do this you really have to get someone who knows how to cancel out brassy tones. You do not want to get a base lifted and end up with a “hot root” or a brick red base color. This is when a true color specialist has to do work like this on a darker base. It takes knowing color base chemistry and how what levels to lift and what undertones to work with. Knowing the laws of color. Believe me its a combo of knowing the chemistry and having good instincts.
For example my friend Leslie came in last week and let her hair go for about 6 months just from being busy etc.. She is a natural level 4 and I had to go in and do a base color with organic hair color by all nutrient and lift her a few levels. Then I went in with foils and blended her color with highlights. The result is a blended multi-tonal blonde. Notice her color is soft and blended. No harsh yellows, or brassy. The hair is not damaged due to the fact that I used ammonia free hair color and low ammonia lightener on the highlights. The hair comes out shiny and feeling better. Now Leslie will have to come in once every 6 to 8 weeks for her base and every 12 weeks for the highlights. To maintain this is easy with in between base color only appts.