This International Standard specifies letter codes for designation of colours and provides rules for their combination to designate colour combinations. The letter codes are intended to be applied in the technical documentation of industrial installations, equipment and products, and in markings of equipment and products. This basic safety publication is primarily intended for use by technical committees in the preparation of standards in accordance with the principles laid down in IEC Guide 104 and ISO/IEC Guide 51. It is not intended for use by manufacturers or certification bodies. One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its publications. The requirements of this basic safety publication will not apply unless specifically referred to or included in the relevant publications. This International Standard does not specify any requirements for the encoding of colour properties, nor for their visual representation. Such requirements are under the responsibility of the different technical committees.