FRANCES SCHULTZ: It's amazing how many people today want to live with a summery, coastal style year-round. How did you make this Southampton house so light in summer and cozy in winter?

ASHLEY WHITTAKER: The house really works year-round. I used lots of bright colors but made sure to integrate plenty of warm materials like velvet and cashmere. A beautiful linen chintz always works, because the fabric feels cool but the colors can be warm. This house has a sense of coziness, and I think that's due to the range of textures we used. A colorful cashmere throw over the back of a sofa or on the arm of a chair adds instant warmth to an otherwise summery room. Velvets have also become an all-season staple. I also love a summer house with a fireplace or two -- and I made sure there was a really comfortable spot in front of the fire to sit and put your feet up.

In the family room -- velvet! Sisal! Ikat! Paisley! Wicker! Is this room the theme song for the house?

That's funny, I guess you could almost call it that. It's the central access from which many of the rooms in the house grew. I'm crazy about all of the blues. What I love in particular are the two prints, the ikat and paisley, that work together but don't compete. We added a navy velvet chair this summer and I love it with the ticking contrast and buttons. It's the layers that make it cozy. The wicker garden stools, tortoise mirror, bamboo blinds, a cashmere throw. The cohesiveness of color is what makes it calm and inviting.

Explain a bit about the layout of the house and how the public rooms had to work together, because with today's open floor plans, it's a common conundrum.

When you enter the house there are four rooms that come into view -- living room, dining room, sunroom, and kitchen. We wanted them to work together but not "match." The blues tie the rooms together, but what really makes it all pop is the pink, coral, and yellow you see in the sunroom beyond.

That turquoise -- and -- white linen on the dining room walls is dreamy.

I know, I love it. One dreary winter day my client and I had driven out to the house to meet. We had chosen the turquoise linen for the sunroom, but when I walked through the dining room and held the sample up to the wall, we both said, "That's it!" The turquoise brightened even the grayest of February days. It has great impact and sets a tone for the colors throughout.

Brown furniture has become the stepchild of design -- yet you've embraced it warmly in the dining room, plunking down that big mahogany table.

My client is crazy about Regency furniture, so this was an obvious place for a big mahogany piece. I love it with the white chairs. And the one thing she knew she wanted in the living room was the faux-tortoise coffee table from Todd Romano. It was the first decision, which helped set the level of sophistication of the room.

The furniture in the living room and in the family room is all very traditional and comfy-looking, but it has a modern, tailored feel.

The shapes are all rather traditional -- the Billy Baldwin–inspired slipper chairs, the tufted ottoman by the fire, the Napoleon III chair covered in turquoise cashmere. It's the fabric that feels young. The bright green strié velvet on the sofa is unexpected and makes it less serious than it is.

Is the furniture new? Custom?

With the exception of a few antique pieces, I had the furniture made. Custom furniture is a little more time-consuming up front, but the result is worth the extra effort.

And clearly a strength of yours. Any words of advice?

If you're going to the trouble of having something made, take the time to go look at it before it's finished. That way a good upholsterer can change an arm that looks too high or the pitch of the sofa back if it's not comfortable enough on first pass. And keep in mind that large furniture pieces always look enormous in a crowded workroom. Don't be scared. If it worked in the furniture plan, it'll work in real life.

The breakfast room is so much fun, with its bright blue-and-white-striped rug and wonderful Frenchy-looking chairs.

I love these French café chairs -- they're indestructible and come in a multitude of colors and patterns, so you can really make them your own. I used navy, turquoise, and white in the kitchen to work with the adjacent family room. The colors look fresh against the outdoors.

Furniture arranging is such a knack, and you've got it. What are your do's and don'ts?

Honestly, I don't even think about fabrics or colors until I have a furniture plan in my mind. It really is the most important aspect of designing a great room. First you want to make sure the room will work for its intended purpose. Living rooms need lots of seating areas and small chairs and upholstered stools to pull around. Family rooms need a comfy sofa and always a big ottoman in place of the coffee table. A good furniture plan means you can have three people in a room or 18, and everyone still has a great time.