Groups of working individuals are typically classified based on the colors of their collars worn at work; these can commonly reflect one’s occupation or sometimes gender. White-collar workers are named for the white-collared shirts that were fashionable among office workers in the early and mid-20th century. Blue-collar workers are referred to as such because in the early 20th century, they usually wore sturdy, inexpensive clothing that didn’t show dirt easily, such as blue denim or cambric shirts. Various other “collar” descriptions exist as well.

White collar
The term “white-collar worker” was coined in the 1930s by Upton Sinclair, an American writer who referenced the word in connection to clerical, administrative and managerial functions during the 1930s. A white-collar worker is a salaried professional, typically referring to general office workers and management. However, in certain developed countries like the United States, the United Kingdom, and Canada, a person is assumed to be a white-collar worker when one engages in a highly professional and successful career or works in either an administrative or managerial role.

Blue collar
A blue-collar worker is a member of the working class who performs manual work and either earns an hourly wage or is paid piece rate for the amount of work done. This term was first used in 1924.

Green collar
A green-collar worker is a worker who is employed in the environmental sectors of the economy. Environmental green-collar workers (or green jobs) satisfy the demand for green development. Generally, they implement environmentally conscious design, policy, and technology to improve conservation and sustainability. Formal environmental regulations as well as informal social expectations are pushing many firms to seek professionals with expertise with environmental, energy efficiency, and clean renewable energy issues. They often seek to make their output more sustainable, and thus more favorable to public opinion, governmental regulation, and the Earth’s ecology.

Green collar workers include professionals such as conservation movement workers, environmental consultants, environmental scientists, council environmental services/waste management/recycling managers/officers, environmental or biological systems engineers, green building architects, landscape architects, holistic passive solar building designers, solar energy and wind energy engineers and installers, nuclear engineers, green vehicle engineers, “green business” owners, organic farmers, environmental lawyers, ecology educators, and ecotechnology workers, and sales staff working with these services or products.

Pink collar
A pink-collar worker is also a member of the working class who performs in the service industry. They work in positions such as waiters, retail clerks, salespersons, and many other positions involving relations with people. The term was coined in the late 1990s as a phrase to describe jobs that were typically held by women; now the meaning has changed to encompass all service jobs.

Other classifications
Some job categories involve duties that fall under one or more of the categories listed above, or none of the above. These categories include:

Gold collar – Highly skilled professionals who may be in high demand, such as chartered accountants, surgeons, anesthesiologists, engineers and lawyers.
Red collar – Government workers of all types; derived from compensation received from red ink budget. Also in China, refers to Communist Party officials in private companies.
Grey collar – Skilled technicians, typically someone who is both white and blue collar; an example is information technology workers. They are principally white-collar, but perform blue-collar tasks with some regularity, such as engineers. May also be used to refer to old aged workers after retirement age.
No collar – Artists and “free spirits” who tend to privilege passion and personal growth over financial gain. This term was popularized on the reality game show Survivor: Worlds Apart, which used No Collar (in addition to White and Blue Collar as the tribal divisions); also, people who work, but not for payment.
Orange collar – Prison laborers, named for the orange jumpsuits commonly worn by inmates.
Scarlet collar – Workers in the sex industry
Black collar – Manual laborers in industries in which workers generally become very dirty, such as mining or oil-drilling; has also been used to describe workers in illegal professions.
Virtual collar – Robots performing manual repetitive tasks, both physical as well as virtual.

Source From Wikipedia