As well as defining the various stop categories, the harmonised standard EN ISO 13850 also defines the relevant principles for design regarding the colour specification of an emergency stop pushbutton. An emergency stop pushbutton must be clearly identifiable, easily visible and quickly accessible. For this reason an emergency stop must strictly be red on a yellow background.
There are currently no colour specifications for an area stop pushbutton in any harmonised standard. The only requirement is that it should not be the colour of an emergency stop pushbutton. The colour black on a yellow background has become established throughout industry for an area stop.