Bring the outdoors into your sunroom, regardless of temperature or rough weather, with the biggest windows the architecture can handle and decor that invites you to look outside. A sunroom that's well insulated can be used as a casual living space year-round, but it shouldn't look like a day at the beach in mid-winter. Establish a basic personality for the room and change some decor elements to adapt it to exuberant spring and elegiac fall with colors and textures.
The seasonal greenery and the falling leaves and snow create a dynamic cinema outside sunroom windows. Accommodate all the changes with a crisp interior decor that coexists with the shifting colors and conditions outside. Stick to black and white for a sharp-looking proscenium -- the place before an ancient stage -- to frame the backyard vista. Limestone pavers or polished concrete floors are spare, as are white walls, enormous windows and a white or dark-beamed ceiling. Soften bold black-and-white striped cotton canvas furniture covers by gray-and-white striped throw pillows and a couple of lacy wicker peacock chairs. Shiny black or white enamel coffee and end tables, black lamp bases with white shades and a single explosion of brilliant color in a vase of cut flowers takes a back seat to the all-important view.
Expand the kitchen into the backyard and create a hybrid sun room-chef's solarium for everyday meal prep and dining. Insulate the space with underfloor heating, large thermal windows, skylights and Southern exposure, if possible. Install paver floors for a touch of rustic outdoors and keep cabinets natural wood or paint them a soft color from nature's palette outside. Sage, buttercream, pebble-gray or pale mushroom offer good choices as nearly neutral colors for built-in cabinets and window frames. A big farm table in light wood provides plenty of seating for family and company. Treat the room as an open plan space and add a comfortable conversation area and a stone fireplace -- an all-year hang-out with a blazing winter hearth.
Slipcovers are your secret weapons. Furnish a sunroom with squashy, comfortable sofas and chairs and carpet it with vibrant colors and interesting textures. But you can adapt your all-year space to the seasons with a simple change of fashion. Replace the faded gem-tone velvet slipcovers with cotton chintz or white denim in summer. Swap out the cozy oriental carpet for a summer sisal rug that's more forgiving of feet wet from the backyard pool. Pop a giant white-paper globe shade over the bare bulb of pendant lamp and store the colored glass shade in the garage until the leaves begin to fall in autumn.
If you have just a sliver of a sunroom, keep it simple. The narrow front porch enclosed to be a year-round solarium is elegant in a monochrome treatment, cluttered in eclectic colors and styles. Paint the walls, floor and window frames glossy white, palest smoke-gray or straw. Put grass-mat carpet over it in summer and exchange for a bleached-out rag rug in winter. Set a love seat, painted to match the walls and covered in pale-patterned fabric of the same color against the wall at one end of the room. A single chair and a couple of painted stools with cushions provide seating without taking up much space. Re-purpose a small trunk as a coffee and snacking table with a storage bonus for extra cushions, winter throws or serving dishes. Use textiles that take up no room to celebrate the seasons: plaid blankets tossed over the love seat in winter; leafy decorative throw pillows for summer; hand-woven ethnic fabrics hung between the windows to add cool-season warmth and a filmy sari or length of sheer net draped over one window to cut summer glare.