Source: www.wingfieldfans.org/douglas_wilson/faq_answer.asp?faqcatid=6

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DOUG ALWAYS USES BROWN
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Doug has used brown a few times but the browns that he has used have varied from dark chocolate to light taupe. There are a HUGE amount of colors that can be classified as "brown." Here are the colors Doug has used in his rooms during seasons 1 and 2:

Knoxville: Forest Glen - light green, white
Philadelphia: Valley Rd - light blue, white
Cincinnati: Sturbridge Rd - brown, gold
Cincinnati: Madison & Forest - purple, pink
San Diego: Wilbur St - orange, white
Knoxville: Stubb's Bluff - taupe, black, white
Washington DC: Cleveland Park - orange, white
Austin: Wycliff Rd - purple, blue
Orlando: Winterhaven - red, white, blue
Albuquerque: Gloria Place - blue, gray, white
New York: Sherwood Dr - dark taupe
New York: Linda Court - orange
New Jersey: Lincroft Rd - taupe
Quakertown: Quaker's Way - green, brown
Boston: Institute Road - golden brown, white
Maryland: Villiage Green - gray, white
Maryland: Fairway Court - navy blue, white
Chicago: Spaulding Ave - yellow, black
Colorado: Stoneflower Drive - green, gray
Seattle: 137th St - brown, white
Portland: Everett St - brown, gray
Berkeley: Prospect St - green, brown, orange
California: Peralta St - pink, brown, white
Los Angeles: Willoughby Ave - red, white
Houston: Sawdust St - red, black
Houston: Appalachian Trail - blue, white
Plano: Shady Valley Rd - sage green, white
North Carolina: Southerby Dr - blue, black, white

So Doug has used chocolate brown (which is the brown people think of whenever they say Doug uses brown "all the time") as the main color in three rooms (Cincinnati: Sturbridge Rd, Seattle: 137th St, Portland: Everett St) and as accent colors in three more (Quakertown: Quaker's Way, Berkeley: Prospect St, California: Peralta St). Using chocolate brown in 6 out of 28 episodes hardly makes it a signature color.