Why you need it: There comes a time every spring or summer when a flaming orange, bright blue or flamboyant violet mani-pedi just makes sense. Embrace the moment -- especially if you're going on vacation and/or wearing a sundress with sandals.

When to wear it: At the beach, at the pool, and whenever you need a dose of optimism.

Try...

Sally Hansen Color Therapy, Ja-Cozy, $7. An argan oil-infused nail polish in the most cheerful shade of cobalt.

OPI Nail Lacquer, Never a Dulles Moment, $8. OPI's latest collection, inspired by the show "Scandal," includes this opaque, sunny yellow.

Orly Gel FX Gel Nail Color, Invite Only, $5. Green is the 2017 Pantone Color of the Year; why not try a Kelly green mani?

Why you need it: Pastels may make you think of spring, but they're beautiful against winter whites and sun-tanned summer skin, too. Pastel nail polish gives any manicure a ladylike, clean look, and they're a beautiful base for nail art.

When to wear it: When you're tired of pale pink or nude; for Pinterest-worthy nail art. (Ombré! Polka dots! Stripes!)

Try...

JinSOON, Aero, $18. Picture this hip sky blue against light-colored denim -- gorgeous, right?

China Glaze, Partridge in a Palm Tree, $7. Milky mint is a pastel hue that always looks fresh.

Floss Gloss Nail Polish, Palazzo Pleasures, $8. This dusty lavender is the darker side of pastel, with just enough gray to look hip and modern.

Why you need it: Gemstone-inspired polishes look rich and sophisticated. They also have the benefit of being almost universally flattering, capable of brightening almost any complexion. Who doesn't shine in shades like emerald, turquoise or pink tourmaline?

When to wear it: With special-occasion outfits, especially in the cooler months and for evening events.

Try...