As the top fashion guru at celeb-mad InStyle, Hal Rubenstein evaluates red carpet looks from Cannes to Chelsea. This made him uniquely qualified to pen “100 Unforgettable Dresses” ($35, Harper Design), an essay- and photo-filled book on 20th- and 21st-century frocks that rocked, from Elizabeth Hurley’s Versace safety-pin dress circa 1994 to Kate Middleton’s wedding gown from earlier this year. We chatted with him about the book and about not dressing like a wallflower this holiday season.

What makes a dress unforgettable, the clothes or the woman?
You can’t separate the dress from the woman, the place and the time. It’s really sort of an amalgamation of the right woman, the right dress and the right time.

And you start the book with Elizabeth Hurley and that crazy safety-pin style. Why?
I thought about clothes that were game-changers. That dress shows the power of a dress to make a woman famous overnight.

These women — Grace Kelly, Tilda Swinton — all seem to know how to dress for the occasion.
These woman took the time to look at themselves and decide what made them special. But it’s funny that we live in a society that wants Angelina Jolie’s lips and Jennifer Aniston’s hair. Women shouldn’t try to be somebody else.

Well, how can we look good and still like ourselves?
Nobody in the world looks like you or has your personality, so start by asking, ‘What are my best features?’ Then dress to accentuate those.

Do women make party dressing blunders this time of year?
During the holiday season, women run to black. You go to an event, and it’s a sea of black. It’s a safety zone. But why would you spend two hours getting dressed to walk into a party and vanish?

Is a colorful party dress the solution to that blandness, then?
Yes, I think if you find a color that makes you happy. The women in this book wanted to stand out. And wearing color says, “You will notice me.”

What if I have no clue what’s good for my coloring or bod?
Find a good salesperson. It helps to read magazines like InStyle, but a good person in a store can give you an independent opinion.

Do you think all that red-carpet dressing stresses out celebs?
The thing about the red carpet is that everybody knows the level of spectatorship in it now. Every single time an actress goes out, she gets judged. She can’t just throw things on, because we’re all snapping, watching and blogging.

Is it better to dress to blend in, then?
Why would you dress to blend in? It’s a mistake because you’re denying people the chance to get to know you.