Designer Joan Osburn knows color. In fact, she consulted on the Sunset book, "Color for Your Home."

"There are secrets and magic with color," said Osburn, who has been a professional designer and color consultant for 27 years. "It's the least expensive way to give your house a lift. It also can be your biggest mistake."

Osburn and her husband, Steve, own Osburn Design in the San Francisco Design Center, but locally are well known for their Napa coffee house and decor shop, Cafe Society, which they closed in 2006 to pursue other design opportunities. The Osburns still run the Parisian wares company from the Design Center and have launched a Web site, cafesocietystore.com, to sell their European finds on the Internet.

Seated in her self-described Provence-yellow living room in Napa, Joan Osburn said, "Color is layered and complex. It can be tricky. It's important to remember that color and light go together. They change at different times of day and year, in natural or artificial light."

How do we determine the best color to use on our walls, floors and furniture?

"With planning and careful thought, color is a step-by-step process. The process is important in every project because the process gets to the result, the product."

Osburn says most people think about paint when they hear the word "color." She stresses that everything; the floor, the ceiling, trim, lights, window coverings and fabrics all have color that must be considered.

She says she's often asked by clients, Where do you start?

"My process is simple, ... I gather the givens. What I mean by that is, whether you're just repainting a room, remodeling or building from scratch, with each project you have givens of furniture, artwork or architecture.

"Color is hard to pin down verbally. Is it avocado or sage? So, I have what I call my color Rorschach Test (from the inkblot test used in psychological evaluation). I have over 1,000 colors and ask clients to pick out the colors they like. People always have color preferences."

Clients often surprise themselves by telling Osburn that they don't like a certain color, such as green -- but then find a shade of green that they do like.

"From there, I divide the colors into warm and cool, gradations of light and dark, bright and dull. At this point, we ask what the givens are in the project because other colors have to work with the givens, whether the givens are the floor color, the lighting or hardware.

"I begin by hunting and gathering. We take the color preferences and the givens, because everything lends color to the space."

A member of the American Society of Interior Design, Joan Osburn is also on the board of Philanthropy by Design and an alumni trustee of the Napa Valley Opera House. She studied painting in Paris and at Cal Arts in Los Angeles. She still paints and creates sculptures.

Color is not given the emphasis it deserves in design school, says Osburn, who studied under the acclaimed designer Rudolph Schaeffer at the Rudolph Schaeffer School of Design in San Francisco.

Schaeffer wrote, "We have to delve into the secrets of color. The reason color study is so important is because color is differentiated light and we can't live without light."

He founded his design school in 1926, and attracted teachers and students from around the world with his philosophy of color and combing the aesthetics of the Arts and Crafts Movement and Asian Art.

When Osburn was his student, he was a lively 94-year old. "He influenced me in so many things," explained Osburn.

Schaeffer taught Osburn to embrace color and how to explain color to her clients. For example, the color wheel confuses many people. Do you choose opposite colors on the wheel or ones that are side-by-side?

"People have to remember is that most color wheels are pure color; they are intense red, blue and yellow. You alter the brightness with different values. What's important is how you react to the combination of color. You can do anything and all will work in an interior. This is where the magic comes in. If you have a darker color, you can pair it with a mirror, even a whole wall of mirrors, which reflect the color and makes the space bigger."

There's no "rule" about the ceiling being white, either.

"You can make the ceiling a lighter shade of the wall color by coming up two values. Color has a trick based on light; the wall color on the ceiling will appear darker. Two values up will make it look lighter. Color is really fun. It makes people happy."

She was a member of the Color Marketing Group for a number of years. This 1,500-member organization advises industries from car manufacturers to paint manufacturers what's going on in the world of design and where color is going. They make color predictions from 18 months to three years into the future.

"We create palettes and name colors," said Osburn. "There are so many different ways to use color. In this country, 10 or 20 years ago, we were about beige. We have a history or being conservative and afraid of color. Things are changing so much. For that, I think we have Steve Jobs to thank. Color Macs and iPods brought color to the masses."

Color preferences can be regional, with East Coast residents preferring blues and grays. Here, warm colors reflect our lifestyle.

"I think of yellow as a neutral. To me, brown is the 'B-word.'"

Osburn says the biggest trend in color is the finish. Special effects can be created using metallic or pearlescent finishes which take the light and shift it, making it more like art or a painting than flat color.

"You can also shift colors," said Osburn. "Take a dark color, even black, and within it there can be a purple or green cast. Play with that and shift it. This is called 'cameu,' a technique of taking two or three tints of a single color. From orange, you might go yellow orange. Shift the other way, and you'd go toward red. It's nuanced."

"Brush-out," the term interior designers and painters use to describe testing different color paint on walls, is the advice she offers do-it-yourselfers.

"It's a mistake to pick a color from a little sample. You can buy less than a quart of paint. Do a brush-out so you don't get a big surprise. A paint chip is ink, not paint, on paper. It's a whole different material. Put the brush out in corners and walls and stand in the center of the room so you can see if all the colors look good together. You can make mistakes because color can be complicated. Don't paint it flat, have sheen. Flat absorbs the light, sheen can bounce the light around, so go over it with a gloss."

Osburn understands people's hesitation.

"It's easy not to do something if you don't know how to start. But remember, it's fun and you can always paint over a wall.