The Code calls for the shell material of the hood to match the robe, and for the colour to be black regardless of the colour of the robe being worn. The interior lining – generally silk – displays the colours of the institution from which the wearer received the degree, in a pattern prescribed by it (usually, if more than one colour is used, chevrons or equal divisions). The opening of the hood is trimmed in velvet or velveteen. In most American colleges and universities, the colour of the velvet hood trimming is distinctive of the academic field – or as closely related as possible – to which the degree earned pertains (see "Inter-Collegiate colors"). Many institutions, particularly larger ones, have dispensed with the bachelor's hood at commencement ceremonies altogether, though a graduate is still entitled to wear one once the degree is conferred.