Now that fall has arrived, the leaves have started to turn bright yellow, deep orange and velvety red.

So why are you still wearing that sparkly blue nail polish?

Changing seasons are a great excuse to update your look. Forget about a whole new wardrobe – slicking on a coat of lip gloss or digging your nails into a new polish can feel as good as a buying a new cashmere sweater. OK, maybe not that good, but for less than $10, it beats faux leopard barrettes.

Choosing to spruce up your look with a new shade is easy. Figuring out what shades work for you is the hard part. And then there’s the whole “fall look” thing.

If you want to follow trends, shelling out $5.95 for a chartreuse eyeliner beats spending $100 on a plastic python-print jacket that probably will be out of style before the snow flies. But do you really want to wear chartreuse eyeliner? What will your boss think?

These are questions for a pro, so I enlisted the help of Alixandra Williams, a makeup artist from Bangor, to translate the trends into a palette you’d actually wear.

As for the chartreuse? “It’s futuristic. It’s fun,” Williams said. From L’Oreal’s On-The-Loose Shimmering Powder in Tart to Estee Lauder’s subtler Pistachio Two-in-One eye shadow, this acid green that resurfaced in Givenchy’s 1998 fall line is still around. It’s great for teen-agers and early twentysomethings. Great for going out dancing. Not so great for the office.

As Kermit said, it’s not easy being green – and it’s not easy wearing it, either. Darker, olive skin tones look great in green shades, though, and toned-down, khaki-greens are more prevalent this fall. Cover Girl’s Field shadow trio and khaki nail polish have soft, sage undertones. L’Oreal’s Mint Showers nail lacquer is a shimmery silver just this side of green. Feeling bold? Try Maybelline’s Expert Eyes shadow duo in Green Glam.

The dark, purplish reds Chanel’s Vamp made famous are still going strong – just check out Lancome’s “Instinct” line, with blackberry lipstick, pale face powder, liquid-stained cheeks and lacy eyebrow “tattoos.”

“This is a fantasy look,” said Williams, a self-confessed hater of the dark “vampira” shades. “Women get tripped up on dark colors. It’s less about confidence and more about skill.”

So if you have great skin, a steady hand and the right foundation, go wild with MAC’s stay-all-day Underworld lipstick, available online at www.maccosmetics.com. Otherwise, tone it down with a glossy lipstick, such as Clinique’s Blac Honey. Or, keep the blackish reds and purples confined to your manicure with Lancome’s deep berry Profond Sommeil, L’Oreal’s flat onyx Black Box, or Revlon’s classic Vixen, a Vamp knockoff.

This fall, pure, movie-star reds are a glamorous alternative to the deeper shades. It all started with Chanel’s Glossimer in Pulsar, a cellophane-clear, sparkly red. For a similar look, try Estee Lauder’s High-Shine Lip Lacquer in Candy Glaze, or MAC’s Lip Glass in Succulent. Want something with a little more substance? Try Elizabeth Arden’s Exceptional Semi-Matte lipstick in Blush Pink, a pinkish red in a formula that rivals MAC’s staying power, or Cover Girl’s Red Rush. Lancome’s Extrait De Vie, a liquid stain, does double duty on the lips and cheeks.

“Women should never shy away from red,” Williams said. “If you’ve got a red lipstick on and just a little mascara or eyeliner, you are dressed.”

For nails, Yves St. Laurent’s Pure Colour Lacquer in Copyright Red is a beautiful basic, and Revlon’s Go Chili kicks classic red up a few notches.

Browns, traditionally more subtle neutrals, are bigger and bolder this season. Estee Lauder’s shimmering Two-In-One Eyeshadow in Brown Shimmer is a coppery-coffee shade that looks as good on as it does in the package. L’Oreal’s Jet Set nail lacquer in Birchwood is a rich, creamy toffee shade, and Revlon’s Toast of the Town lipstick is “a beautiful brown,” Williams said. It helps to have yellow undertones in your skin – not everyone can wear true browns well.

Beige, on the other hand, is “a good, quick slick,” Williams said. It’s neutral, it’s simple and it’s virtually impossible to screw up. Beef it up with a bit of lip liner, though, if you’re going to wear beige lipstick. MAC and Revlon both make shades called Spice that are pretty neutrals that will keep your lips from fading away. On the eyes, try Clinique’s No Show Taupes – perfect.

The soft pinks and burgundies Williams has seen in her travels to Boston this season are flattering for most any complexion. Maybelline’s Expert Eyes duo in Beaujolais is soft and pretty. Jane’s Purple Heart shadow is deep, shimmery and affordable enough for teens, but adults will like it, too. Craving a fine wine? Try Mary Kay’s Feisty nail polish and lip crayon.

Still can’t find a shade to suit you? Don’t worry. Revlon and Physician’s Formula both have little lipstick kits with four colors you can mix to create your own, personal favorite.

“This is a great idea. It’s a really cool tool,” Williams said. “You could probably mix a gazillion colors. This is what makeup artists do.”

You don’t need to be a makeup artist to make fall’s trends work for you. Just pick your favorite color group and try something new. Even if you don’t like it, you’re only out $5, which is more than you can say for the cashmere sweater.

Makeup artist Alixandra Williams offers the following tips:

. To find the right lipstick shade, pinch the tip of your index finger. Choose a color that’s a few shades darker.

. If you wear matte lipstick, make sure your lips are moist, not dry and cracked.

. Vaseline, Eucerin or Kiehl’s lip balm work wonders on chapped lips. To slough off dry skin, slather some on after showering, wait five minutes and brush your lips gently with a soft toothbrush.

. The dark wines and violets look best on olive skin tones.

. Older women look great in brighter shades – corals, hot pinks and pinky-purples.

. The Olympics may be over, but go for the gold anyway. Silver, the shade of the new millennium, has been edged out by gold, the shade of chains, charms and rappers’ teeth. Almost everyone can wear gold – it gives a soft, warm glow. Try it out in the ubiquitous fairy dust – the loose, shimmery powder-in-a-pot that’s everywhere.

. Just because it costs less doesn’t make it any less cool. For less than $5, you can’t beat Wet ‘n Wild, with its trendy shades (their Twist-Up Blush Stick in Flirt, which costs $2.99, is a dead ringer for NARS’ Malibu, an opalescent blusher that costs more than $25).

. Even if you’re going for a “natural” look, a great lipstick will enhance your natural glow.

. Don’t forget the lip liner, in a subtle, similar shade to your lipstick. And blend – the two-tone lip is out.