Short answer
Concrete is grey because ordinary Portland cement contains small amounts of iron, manganese, chromium and other transition metals that colour the paste; white cement keeps them very low. The finished colour then depends on the sand and aggregate, the water content, the formwork, curing and any pigment, all of which vary between pours. It darkens when wet, blooms white with efflorescence, and weathers by losing surface paste — so colour matching concrete is about controlling the mix and process, and accepting a range.
Relative to other materials in this section, not a measurement of a particular product.
| Process | What you see | Driven by | Slowing it |
|---|---|---|---|
| Efflorescence | White bloom or streaks | Soluble salts carried to the surface by water | Limit water entry; dry-brush early bloom |
| Soiling and weathering | Darker streaks under sills; exposed aggregate as fines erode | Run-off patterns and erosion of the surface paste | Detail drips and sills; penetrating sealer rather than a film coating |
The colour of plain concrete is mostly the colour of the hardened cement paste coating every grain of aggregate. Ordinary grey cement gets its greenish-grey to brownish-grey tone from transition elements in the clinker — chromium, manganese and iron have the strongest effect — carried in from the limestone and clay. White Portland cement is made from raw materials chosen for very low contents of those elements, which is why it costs more. Pigments for coloured concrete are overwhelmingly iron oxides (reds, yellows, browns, blacks), with chromium oxide for green and cobalt blue at a premium; they tint the paste rather than the aggregate, so the effect is stronger and cleaner on white cement than grey, where the paste's own grey mutes it.
Concrete is a material made on site from variable ingredients. The same nominal mix can differ in colour between deliveries because of cement from a different kiln run, sand of a slightly different colour, more or less mix water (wetter mixes cure lighter), changes in curing temperature and humidity, different form-release agents or formwork absorbency, and the time at which the surface was finished. The US National Park Service's guidance on repairing historic concrete stresses trial mixes that account for aggregate and paste colour, forming and finishing, assessed after curing — and notes that the hardest part of matching old concrete is reproducing its variability, not a single colour.
As-struck concrete shows the paste skin formed against the mould, with the mould's texture — smooth plywood, board-marked timber, rubber liners. Acid-etching, abrasive blasting and exposed-aggregate finishes remove that skin to reveal sand and stone, so the aggregate's colour takes over: a grey concrete with golden gravel reads warm once exposed. Polished concrete floors are ground through the surface, again revealing aggregate, and then densified and polished to a sheen that deepens the colour. Film-forming coatings change colour and can hide board marks; penetrating sealers and pigmented stains alter colour less and keep texture, which is why conservation guidance prefers them for adjusting old concrete.
Cement is a major source of soluble salts. Water moving through young concrete carries them to the surface, where they dry as white efflorescence — most visible on dark and pigmented concrete, and usually heaviest in the first months. Over years, rain erodes the thin surface paste on exposed faces, slowly revealing the sand and making the surface slightly lighter and rougher, while sheltered areas collect soot and organic growth and darken. The streaks under window sills and copings follow the water. These changes are part of why a concrete building looks different at five years than on handover, and why detailing drips and run-off is a colour decision as much as a technical one.
Why: Changes in cement batch, sand, water content or curing between deliveries.
Fix: Fix the supplier and materials, control water and curing, and pour visible areas continuously where possible.
Why: Efflorescence masking the pigment.
Fix: Let early bloom dry and brush off; limit water movement; avoid acid washes that can etch the surface.
Why: Mix, aggregate exposure or surface finish differs from the original.
Fix: Develop trial mixes and finishes on site and judge them only after curing.
Each statement is labelled by kind — established fact, a standard’s requirement, observed market data, a convention, or Colourwise’s own interpretation or analysis — with the strength of the evidence behind it.
FactModerate evidence
The grey colour of ordinary Portland cement comes from transition elements such as chromium, manganese and iron in the clinker; white Portland cement is made with these kept to very low levels.
Source: White Portland cement
FactStrong evidence
Matching repair concrete to historic concrete requires trial mixes that account for the types and colours of aggregate and paste, and different forming and finishing techniques, assessed after curing.
Source: Preservation Brief 15: Preservation of Historic Concrete
FactStrong evidence
Film-forming coatings often change the colour and appearance of concrete and can hide surface texture; pigmented penetrating stains are an alternative for adjusting colour.
Source: Preservation Brief 15: Preservation of Historic Concrete
FactModerate evidence
Concrete and concrete products can contain several times more soluble material than fired clay and are a principal contributor of the salts that form efflorescence on masonry.
Source: Technical Note 23A: Efflorescence — Causes and Prevention (June 2019)
Reviewed 29 September 2026. Colourwise summarises its sources in its own words and does not reproduce standards text or proprietary colour data. Spotted an error? Tell us.