Pale crag martin to do so, it would cast doubts on their specific distinctness. There are several subspecies differing in plumage shade or size, although the differences are clinal, and races interbreed where their ranges meet. The pale crag martin of the nominate subspecies "P. o. obsoleta" is 12–13 cm (4.7–5.1 in) long with light brown upperparts, becoming paler on the lower back, and a short square tail that has small white patches near the tips of all but the central and outermost pairs of feathers. It has a pale grey throat, upper breast and underwing coverts, and the rest of the underparts
Palatinate (colour) The precise colour of palatinate purple used by the University varies a good deal. Its most long-established usage is in the University's academic dress and sporting colours, both of which use a significantly paler shade than that used by the university for corporate purposes. The palatinate purple used for the academic robes is said by Shaw (1966) to be British Colour Council No. 177 "Crocus" from the second (1951) edition of the "Dictionary of Colour Standards". The shade of purple used by Durham University in its corporate branding, as of 2017, is: Pantone number 255C; CMYK: 51, 91, 0, 34;