She’s frosted Beyoncé’s tips, persuaded Michelle Williams to turn her pixie platinum, and dyed Katy Perry’s locks every shade of the rainbow. The entertainment industry’s most coveted colorist, Rita Hazan explains how to work the salon system and why someone might pay $20,000 for a color.

Is there a rule of thumb for finding your best shade?
If you have olive or dark skin, your hair should have honey undertones. If you’re fair, opt for red undertones. If you have a medium skin tone, you can go in either direction. Try full-out fiery red only if you have very pale skin and light eyes.

What’s the strangest thing you’ve been asked to match a hair color to?
People save locks of hair from their first cut as a child, then ask me to bring them back to the color of their youth. They actually hand me their baby ponytails.

Your biggest pet peeve?
When clients ping-pong between colorists. It has absolutely nothing to do with loyalty. If you’re not seeing one colorist consistently, you’ll never get a good balance of tone, because every stylist uses a different process.

But what if you travel a lot?
I give my best clients a bottle of my formula and write down the instructions so they can get their hair done elsewhere without ruining the color. That tends to be hard info to pry out of colorists’ hands, but we may budge if we know you’ll be out of town.

It sounds like quite a symbiotic relationship.
The best clients who see me regularly always tip more than 20 percent and are generous with sharing their job perks—like designer clothes or tickets to shows—so they get first crack at my appointment book. I’ll see them early in the morning or very late at night and throw in extra treatments free.

Speaking of the appointment book, is there a particularly desirable slot?
Ask for the last appointment of the day to get the most attention. Stylists will be able to spend more time with you knowing that they don’t have another client waiting.

What’s the rudest thing you can do in a salon?
Leave coins as part of your tip.

What should you expect to spend for a quality coloring?
From $250 to $350 is reasonable, but high-profile clients will shell out $20,000 to fly colorists to another country and put us up for a few days just to do their highlights. Promise me a sink and I’ll be there!

Rita Hazan's Expert Product PicksCourtesy (3)

Bonus! Hazan spills on how to keep color fresh between visits with her secret touch-up weapons:

1. Rita Hazan Root Concealer in Light Brown (above, left), $25; ritahazan.com.
Dust this colored powder onto your scalp to hide roots.

2. Shu Uemura Art of Hair Full Shimmer Illuminating Shampoo ($48) and Conditioner ($58); shuuemuraartofhair-usa.com.
Shu Uemura’s shampoo and conditioner are super hydrating for color-treated hair.

For more pros’ tips, tricks, and best-kept secrets, pick up a copy of InStyle’s July issue, on sale and available for digital download now.

In need of more hair inspiration? Check out all the celebrity hair makeovers of 2014 in our gallery!