The first mention of it is in Tractate Shabbat , which discusses respect and fear of God. Sephardic communities generally did not have the custom of wearing a kippah all the time. Some diaspora Jews leave off the kippah at school, work, or when testifying in court, because of real danger or uneasiness in appearing in the secular world with an obvious symbol of Jewishness. In Israel wearing a kippah also has a social significance. The style of kippah in Israel can also indicate political and religious affiliations.
Classical orthodoxy uses a large, smooth, black one shaped like a bowl.
Another play on this rebellion is to wear a knitted black kippah. This is also usually used to confuse people as to where you stand. In Bukhara and the Caucasian Mountains the use of a large brightly woven kippah is common. It is similar in shape to a cantor's kippah without the peak. This custom can also be found in other Sephardic communities.