Usually, the colours are allocated randomly. However, the 180/184 was allocated the Purple line when the services were made into an Overground route in 2004 and the 184 was extended to Huddersfield replacing service 365. The extension also saw the 184 service incorporated into the Huddersfield Overground with services 348, 350 and 352 (which were later replaced by routes 181, 182, 183 and 185 to fit in with the 184) already branded as the Purple line (as had the 365 previously).