Know when to go lighter or darker. The rule is as follows: For permanent dye, choose a color a smidge darker than what you want because of the strong developer, says Ionato. With semipermanent dye, however, err on the lighter side of the color you're looking to achieve. "Semipermanent formulas don't have a developer, meaning they get darker and darker the longer you leave them in your hair," says Ionato. "It's safer to choose a color that's a bit lighter from the get_go."
Similar to Hair Color, the Hair Color Booth app lets you experiment with your hair colour in crazy shades. You can also select just some of your hair to try different colour streaks or ombre colour combinations. This is a great app to freak out your mum or friends too! There's only a few colours in the free version but it's enough to try some rainbow hair.