This Recommendation ITU-T L.1203 defines the requirements and guidelines for DC power distribution identification by colour and marking in Telecom/ICT installations (wire, cables, electric distribution boards, interconnections, etc…). It avoids confusion and errors between the different AC and DC power interfaces and distributions used in the building and inside Telecom/ICT systems, as 400VDC power feeding interface standardized in [ITU-T L.1200] is more used for many reasons among which, increased power density of ICT equipment, energy efficiency, simplified reliable power feeding architecture, costs optimisation. Recommendation ITU-T L.1203 is helping for a progressive introduction of up to 400VDC installations in cohabitation with existing -48V and AC distribution.