How to Match Paint Colours Perfectly: Spectrophotometers, Fan Decks and Sample Pots

Why Colour Matching Matters

In decorating, few things are more frustrating than a colour that does not quite match. Whether you are touching up a damaged wall, extending a colour scheme into an adjacent room, repainting a single wall after repairs, or trying to recreate a colour seen in a magazine or a friend's home, the ability to match paint colours precisely is a skill that separates professional results from amateur approximation.

In London, where period properties often feature carefully considered colour schemes that have evolved over decades — and where decorators may be asked to match a Farrow & Ball colour from 2008 in a Little Greene product, or to replicate a faded exterior colour in a fresh coating — colour matching is a daily requirement.

The Spectrophotometer: Precision Colour Reading

A spectrophotometer is a handheld electronic device that reads the precise colour of a surface by measuring the wavelengths of light it reflects. Professional-grade instruments — such as the Datacolor ColorReader, the X-Rite Capsure, or the NCS Colourpin — analyse the surface and output a colour reference in one or more colour systems: NCS, RAL, or the proprietary palettes of major paint brands.

How it works: the device emits a controlled burst of light onto the surface and measures the reflected spectrum. It then compares this spectrum against its database of known colours and identifies the closest match. The best devices achieve accuracy within a Delta E of 1 — a colour difference imperceptible to the human eye.

When to use it: spectrophotometer matching is most valuable when you need to identify an unknown colour — for example, matching an existing wall colour that has no remaining paint tin or colour reference. It is also useful for matching colours across brands: identifying the Farrow & Ball equivalent of a Dulux colour, or the RAL code of a powder-coated window frame.

Limitations: the accuracy of a spectrophotometer reading depends on the condition of the surface being measured. Faded, dirty, or glossy surfaces will produce inaccurate readings. For best results, measure an area that is clean, undamaged, and representative of the original colour — behind a picture, inside a cupboard, or under a light switch plate.

Fan Decks: The Decorator's Reference Library

A fan deck — the fanned collection of colour swatches produced by each paint manufacturer — remains the most practical tool for colour selection and matching in everyday decorating. Professional decorators in London carry fan decks from the brands they use most frequently: Farrow & Ball, Little Greene, Dulux Trade, Benjamin Moore, and others.

Using a fan deck effectively:

• Hold the swatch against the surface in the light conditions of the room. Colour appears different under natural daylight, incandescent bulbs, LED panels, and fluorescent tubes. The colour that looks right under the showroom's spotlights may look wrong in a north-facing London living room.
• Compare at arm's length rather than pressing the swatch against the wall. A small gap between swatch and surface allows the eye to judge the comparison more accurately.
• Narrow down to two or three options and request sample pots of each. A fan deck swatch is too small to judge a wall colour definitively — it provides direction, not confirmation.

Cross-brand matching: if you need to match a colour from one brand in another brand's range, fan decks from both brands can be compared side by side. This is imprecise but useful for narrowing the search. For greater accuracy, use a spectrophotometer to read the source colour and identify the closest match in the target brand's database.

Sample Pots: The Essential Confirmation Step

Sample pots — small tins of paint, typically 75ml to 125ml — are the final and most important step in colour matching. No colour decision should be made without testing the actual paint on the actual wall in the actual room.

Best practice for sample testing:

• Paint a large area — at least A3 size, ideally larger. Small swatches are misleading because they are overwhelmed by the surrounding colour.
• Paint on the wall itself, not on a piece of card held against it. The texture and porosity of the wall surface affect how the colour reads.
• Apply two full coats at the correct spreading rate. A single thin coat over a different background colour will not show the true colour.
• Test in multiple locations — a colour that works on the chimney breast may look different on the window wall, where natural light hits it differently.
• View at different times of day. Morning light, afternoon light, and artificial evening light all change how a colour reads. A warm neutral that looks perfect in afternoon sunlight may look cold and grey under LED downlights.

Common Colour Matching Challenges in London

Several situations recur in London decorating projects:

Matching faded colours — an exterior colour that has been exposed to UV for years will have shifted significantly from the original. A spectrophotometer reading of the faded surface will match the faded colour, not the original. The solution is to find a protected area — under the eaves, behind a downpipe — where the original colour survives, or to consult the manufacturer's historical records if the original specification is known.

Matching across finishes — the same pigment mix in a matt emulsion, an eggshell, and a gloss will appear as three different colours because sheen level affects how light interacts with the surface. When matching a wall colour to a woodwork colour, allow for this difference.

Matching batch variation — paint is manufactured in batches, and slight variations between batches are normal. For a large project where colour consistency is critical, buy all the paint at once and intermix tins (boxing) before application.

Matching heritage colours — London's conservation areas and listed buildings sometimes require colours to match historical specifications. Paint analysis — a laboratory examination of successive layers of paint on a sample — can identify the original pigments and formulations used, allowing a modern equivalent to be mixed.

The Professional Approach

Professional decorators in London combine all three methods: a spectrophotometer for precision identification, fan decks for selection and comparison, and sample pots for confirmation. This layered approach eliminates guesswork and ensures that the final colour on the wall is exactly what was intended — not a close approximation, but a precise match.