One of the most common questions we get is which colour to use. The honest answer: there is no single written UK standard for the colour of marking paint sprayed onto a surface. What exists are strong conventions, mostly borrowed from the colour codes for the buried services themselves. Here is how the trade generally works — and, just as importantly, where those conventions stop.
Why the surface mark mirrors the service below
Street Works UK (formerly NJUG) publishes colour codes for buried apparatus — the pipes and cables underground, not the spray on the surface. When the ground above a service is marked, it is sprayed in the colour of the thing beneath, so anyone reading the mark knows what runs there before a spade goes in. It is a safety habit as much as a convention: a red line reads as electricity to everyone on site without a word. That is why the surface colour tends to follow the buried-service colour, even though no regulation forces it.
The common colours
- Yellow — gas. Also widely used off-street for warehouse walkways, forklift lanes and hazard hatching.
- Blue — clean (potable) water. Often used for mandatory-action zones and disabled bays too.
- Red — electricity cables, the highest-risk strike. Also fire equipment, danger zones and no-stopping routes.
- Green — telecoms and cable ducting. Also first-aid points, safety equipment and escape routes.
- Black or grey — often drainage, waste water and district heating; black is also the go-to for blacking out superseded lines before a re-mark.
- White — general purpose: proposed excavation outlines, standard bays, road lines, sports pitches and pedestrian routes.
- Orange — no fixed UK utility meaning, which is what makes it useful for high-visibility setting-out, levels and spot marks on dark tarmac where a duller colour would disappear.
Telecoms is the one to treat with caution: buried comms ducting can be grey, white, green, black or purple depending on the network, so “green for comms” is a rule of thumb rather than a certainty. When in doubt, the drawing wins.
Marking floors indoors
Inside a warehouse or unit the same colours carry over by convention rather than by any single rule. Yellow tends to mark walkways and traffic routes, red flags fire and danger, and hatching warns of a hazard. The Workplace (Health, Safety and Welfare) Regulations 1992 require traffic routes to be marked, but do not dictate the colour — that is left to the site and its risk assessment.
Safety colours are a different system
Marking conventions are not the same as safety-sign colours. Red for danger, blue for mandatory and green for a safe condition come from ISO 3864 / BS 5378, which govern safety signage — signs and labels, not floor paint. They overlap with the marking conventions in places, which is handy, but they are a separate system with their own rules.
The rule that overrides all of this
Always follow the colour scheme given for the job. Site rules, the principal contractor's drawings and client specifications come first, every time. These conventions are a sensible default when nothing else is specified — a shared shorthand the trade understands — not a substitute for the scheme on the drawing.