The geometric designs and heavy lines seem to be adapted from the area's textile and weaving patterns. 'In contrast with the sobriety of architecture and decoration in the rest of Arabia, exuberant color and ornamentation characterize those of Asir. The painting extends into the house over the walls and doors, up the staircases, and onto the furniture itself. When a house is being painted, women from the community help each other finish the job. The building then displays their shared taste and knowledge. Mothers pass these on to their daughters. This artwork is based on a geometry of straight lines and suggests the patterns common to textile weaving, with solid bands of different colors. Certain motifs reappear, such as the triangular mihrab or 'niche' and the palmette. In the past, paint was produced from mineral and vegetable pigments. Cloves and alfalfa yielded green. Blue came from the indigo plant. Red came from pomegranates and a certain mud. Paintbrushes were created from the tough hair found in a goat's tail. Today, however, women use modern manufactured paint to create new looks, which have become an indicator of social and economic change.'

The interior walls of the home are brightly painted by the women, who work in defined patterns with lines, triangles, squares, diagonals and tree-like patterns. 'Some of the large triangles represent mountains. Zigzag lines stand for water and also for lightning. Small triangles, especially when the widest area is at the top, are found in pre-Islamic representations of female figures. That the small triangles found in the wall paintings in 'Asir are called banat may be a cultural remnant of a long-forgotten past.'

Color is a powerful design tool in decoration, as well as in interior design, which is the art of composing and coordinating colors together to create a stylish scheme on the interior architecture of the space. It can be important to interior designers to acquire a deep experience with colors, understand their psychological effects, and understand the meaning of each color in different locations and situations in order to create suitable combinations for each place. Combining colors together could result in creating a state of mind as seen by the observer, and could eventually result in positive or negative effects on them. Colors can make the room feel either more calm, cheerful, comfortable, stressful, or dramatic. Color combinations can make a tiny room seem larger or smaller. So it is for the Interior designer to choose appropriate colors for a place towards achieving how clients would want to look at, and feel in, that space. In 2024, red-colored home accessories were popularized on social media and in several design magazines for claiming to enhance interior design. This was coined the Unexpected Red Theory.

Residential design is the design of the interior of private residences. As this type of design is specific for individual situations, the needs and wants of the individual are paramount in this area of interior design. The interior designer may work on the project from the initial planning stage or may work on the remodeling of an existing structure. It is often a process that takes months to fine-tune and create a space with the vision of the client. Other areas of specialization include amusement and theme park design, museum and exhibition design, exhibit design, event design (including ceremonies, weddings, baby and bridal showers, parties, conventions, and concerts), interior and prop styling, craft styling, food styling, product styling, tablescape design, theatre and performance design, stage and set design, scenic design, and production design for film and television. Beyond those, interior designers, particularly those with graduate education, can specialize in healthcare design, gerontological design, educational facility design, and other areas that require specialized knowledge. Some university programs offer graduate studies in theses and other areas. For example, both Cornell University and the University of Florida offer interior design graduate programs in environment and behavior studies.

As department stores increased in number and size, retail spaces within shops were furnished in different styles as examples for customers. One particularly effective advertising tool was to set up model rooms at national and international exhibitions in showrooms for the public to see. Some of the pioneering firms in this regard were Waring & Gillow, James Shoolbred, Mintons, and Holland & Sons. These traditional high-quality furniture making firms began to play an important role as advisers to unsure middle class customers on taste and style, and began taking out contracts to design and furnish the interiors of many important buildings in Britain.In America, Candace Wheeler was one of the first woman interior designers and helped encourage a new style of American design. She was instrumental in the development of art courses for women in a number of major American cities and was considered a national authority on home design.

An important influence on the new profession was The Decoration of Houses, a manual of interior design written by Edith Wharton with architect Ogden Codman in 1897 in America. In the book, the authors denounced Victorian-style interior decoration and interior design, especially those rooms that were decorated with heavy window curtains, Victorian bric-a-brac, and overstuffed furniture. They argued that such rooms emphasized upholstery at the expense of proper space planning and architectural design and were, therefore, uncomfortable and rarely used. The book is considered a seminal work, and its success led to the emergence of professional decorators working in the manner advocated by its authors, most notably Elsie de Wolfe.

Interior designer implies that there is more of an emphasis on planning, functional design and the effective use of space, as compared to interior decorating. An interior designer in fine line design can undertake projects that include arranging the basic layout of spaces within a building as well as projects that require an understanding of technical issues such as window and door positioning, acoustics, and lighting. Although an interior designer may create the layout of a space, they may not alter load-bearing walls without having their designs stamped for approval by a structural engineer. Interior designers often work directly with architects, engineers and contractors.

Interior designers must be highly skilled in order to create interior environments that are functional, safe, and adhere to building codes, regulations and ADA requirements. They go beyond the selection of color palettes and furnishings and apply their knowledge to the development of construction documents, occupancy loads, healthcare regulations and sustainable design principles, as well as the management and coordination of professional services including mechanical, electrical, plumbing, and life safety—all to ensure that people can live, learn or work in an innocuous environment that is also aesthetically pleasing.

Someone may wish to specialize and develop technical knowledge specific to one area or type of interior design, such as residential design, commercial design, hospitality design, healthcare design, universal design, exhibition design, furniture design, and spatial branding. Interior design is a creative profession that is relatively new, constantly evolving, and often confusing to the public. It is not always an artistic pursuit and can rely on research from many fields to provide a well-trained understanding of how people are often influenced by their environments.

he Art Deco style began in Europe in the early years of the 20th century, with the waning of Art Nouveau. The term 'Art Deco' was taken from the Exposition Internationale des Arts Decoratifs et Industriels Modernes, a world's fair held in Paris in 1925. Art Deco rejected many traditional classical influences in favour of more streamlined geometric forms and metallic color. The Art Deco style influenced all areas of design, especially interior design, because it was the first style of interior decoration to spotlight new technologies and materials.

Modern design grew out of the decorative arts, mostly from the Art Deco, in the early 20th century. One of the first to introduce this style was Frank Lloyd Wright, who had not become hugely popularized until completing the house called Fallingwater in the 1930s. Modern art reached its peak during the 1950s and '60s, which is why designers and decorators today may refer to modern design as being 'mid-century'. Modern art does not refer to the era or age of design and is not the same as contemporary design, a term used by interior designers for a shifting group of recent styles and trends.

The interior design profession became more established after World War II. From the 1950s onwards, spending on the home increased. Interior design courses were established, requiring the publication of textbooks and reference sources. Historical accounts of interior designers and firms distinct from the decorative arts specialists were made available. Organisations to regulate education, qualifications, standards and practices, etc. were established for the profession.

Interior design was previously seen as playing a secondary role to architecture. It also has many connections to other design disciplines, involving the work of architects, industrial designers, engineers, builders, craftsmen, etc. For these reasons, the government of interior design standards and qualifications was often incorporated into other professional organisations that involved design. Organisations such as the Chartered Society of Designers, established in the UK in 1986, and the American Designers Institute, founded in 1938, governed various areas of design.

It was not until later that specific representation for the interior design profession was developed. The US National Society of Interior Designers was established in 1957, while in the UK the Interior Decorators and Designers Association was established in 1966. Across Europe, other organisations such as The Finnish Association of Interior Architects (1949) were being established and in 1994 the International Interior Design Association was founded.