"Your natural hair color first determines where to start when you're choosing your desired shade," says celebrity colorist Sharon Dorram, who has worked with Julia Roberts, Kate Hudson, and Nicole Kidman. People with warmer base tones, like Emma Stone, who is a natural blond, can take on different colors than someone with a cooler starting hue. Ask your hairstylist, who will be more attuned to identifying nuanced tones.
2. Be Realistic
Rome wasn't built in a day—and drastic hair color can't be achieved overnight, either. "The more pronounced the change you attempt, the more likely the results will be brassy, ashy or just plain disappointing," says celebrity colorist Kelly Van Gogh. A subtle shift, on the other hand, like Camilla Belle's lift from rich brunet to spicy cinnamon, is completely attainable.
3. Buy More Than You Need
"Depending on the length and thickness of your hair, you should always buy a few boxes of dye," Dorram advises. Someone with below-the-chest strands, like Miley Cyrus, may require three boxes to get full coverage. "It's better to have too much hair dye, than to realize you need more halfway through," she says.
4. Find the Right Formula
Foam dyes like John Frieda's Precision Foam Colour (left) are best for women with sensitive skin, since the mousse-like formulas won't drip onto the face or hairline. According to cosmetics chemist Ni'Kita Wilson, women with thick or curly hair will have better luck with gel or liquid formulas, like Kelly Van Gogh's Master Blend (center) and the L'Oreal Excellence Creme (right), which provide full coverage and distribute efficiently throughout the hair.
5. Steer Clear of the Pool
Chlorine strips away the hair cuticle, allowing minerals in the water to get into the hair shaft and alter your color. Rather than diving in, sit pretty poolside, like Whitney Port, for at least two weeks before and after dyeing your hair.
6. Buy a Shade Lighter than You Want
Take it from Rihanna's colorist Ursula Stephens, who knows a thing or two about fine-tuning tresses: Hair dye always comes out darker than the image on the box. "Buy one or two shades lighter than your desired color," she advises. "It is easier to amp up a color's intensity than it is to tone it down."
7. Skip the Shower
"The scalp's natural oils work as a buffer to prevent irritation," says colorist James Corbett of the James Corbett Studio in New York City. Translation? Dirty hair is ideal for dyeing. "It's also much easier to section second day hair, which ensures even color distribution." He suggests skipping the shampoo a day before you plan to color—and we suggest sporting a cute baseball hat like Minka Kelly's to sweep back unwashed strands.
8. Swap Your Shampoos
Certain shampoos, like clarifying or dandruff-fighting formulas, can strip away hair color with sulfates and harsh chemicals. Get a color preserving shampoo, which is more gentle. We like the Joico K-Pak Color Therapy shampoo and conditioner, which forms a lightweight, protective shield over the hair shaft—and smells great.
9. Prepare for the Damage
Hair always gets a little damaged when applying color, even if you're going back to your natural hue. Both permanent and semi-permanent dyes contain hydrogen peroxide, which chemically changes the color of the hair pigment. Celebrity colorist Tracey Cunningham recommends using the Redken Real Control Intense Renewal Mask at least once a week to moisturize dry hair and restore shine. The mask aids in repairing damaged hair and fortifying strands so they resist further breakage.
10. Don't Dye After 7 PM
Most brands list a 1-800 number on the box that will connect you to a real life hair color expert. However, most of these hotlines close at 7 PM EST on weekdays, and are closed on weekends. Dye during business hours. That way, help is only a phone call away.