The belt lines 3, 7, 9 and 10 were given a line colour in one colour: yellow, blue, green and red, respectively. The radial lines usually had line colours divided into two. Later, new line colours divided into three fields (using a total of two colours) were introduced. Lines 7 and 13 have different combinations again. Line 7 is blue, but for clarity two horizontal white stripes are added. Line 13 is white, but has a pattern of blue squares added. Line 22 (originally 19) (Circle Line Centraal Station) was the only line using the colour pink.