"Taqiyah" is the Arabic word for a Muslim cap used in Saudi Arabia. In Pakistan and India, the prayer cap is called a "topi". Topi means cap in the Hindi/Urdu language. In Pakistan, men usually wear the topi with "salwar kameez". In Bangladesh, it is known as "tupi". In the United States and Britain, many Muslim merchants sell the prayer cap under the name "kufi".
The taqiyah (Somali "Koofi") is a short, rounded skullcap. They are often worn for religious purposes; for example, Muslims believe that the Prophet Muhammad (PBUH) used to keep his head covered, therefore making it "mustahabb" (i.e., it is commendable to cover the head in order to emulate him). Muslims often wear them during the five daily prayers.
When worn by itself, the taqiyah can be any color. However, particularly in Arab countries, when worn under the "keffiyeh" headscarf, they are kept in a traditional white.