Why RAL colours look different on every screen

Open the same RAL colour on your laptop, then on your phone, then on a friend's tablet, and you will see three slightly different colours. None of them is wrong in an interesting way, and none of them is right either. A RAL Classic number refers to a physical colour standard: a painted sample you can hold. Everything you see on a screen, including the swatches on the RAL Classic chart on this site, is a translation of that sample into light, and every screen does the translating a little differently.

This matters most at the moment people decide. Someone picks a colour for a garden gate on a phone at night, orders a tin, opens it in the morning and wonders why it looks nothing like the picture. The tin is usually fine. The picture was never the colour.

A screen makes colour from three lights

A painted surface reflects part of the light that hits it. A screen does something quite different: it emits light from tiny red, green and blue elements and mixes them. The range of colours a given set of red, green and blue lights can produce is called its gamut, and no screen covers everything a paint can show.

Most web colour is described in sRGB, a standard colour space designed for typical monitors. When this site lists a hex value for a RAL colour, it is an sRGB value: three numbers from 0 to 255 for red, green and blue. That gives the screen something to aim at, but the aim depends on the hardware.

• A basic office monitor or an older laptop may not reach the full sRGB range. Saturated greens and blues come out a bit flat.
• Many newer phones, tablets and laptops have wide-gamut panels that reach well beyond sRGB. If the operating system and browser handle colour properly, they show sRGB colours as intended. If something in the chain treats the sRGB value as if it were in the panel's wider space, the colour comes out louder than it should.
• Some RAL shades simply sit outside sRGB. The luminous colours are the obvious case, but a few strong yellows, oranges and greens also get clipped to the nearest colour the screen can make.

So the first reason colours differ is plain physics: different screens have different lights, and some paint colours cannot be built from any of them.

Brightness and white point move everything

Even two screens with the same gamut will disagree if they are set up differently. Two settings do most of the damage.

Brightness

Turn a laptop down to a third of its brightness in a dim room and every dark colour sinks towards black. Turn a phone up to full in sunshine and the same colours lift and wash out. Paint does not change its reflectance when you dim the lights in the room, but your eye adapts to the surroundings, and the screen's own brightness sets how far down the dark end of the scale you can see. Dark greens, greys and blues are the most affected, because the difference between them sits in the bottom tenth of the brightness range.

White point

Every screen has a white that everything else is built on. The sRGB standard assumes a fairly neutral daylight white, but screens drift warmer or cooler with age, factory tuning and user settings. A cool white makes the whole picture bluer. A warm white yellows it.

Then there are the evening modes. Most phones and computers now have a setting that warms the screen after dark to cut blue light: Night Shift on Apple devices, Night Light on Windows and Android, and similar names elsewhere. Some phones also adjust the white balance to match the room using a sensor. All of these deliberately change every colour on the screen. They are good for your sleep and terrible for choosing paint.

Auto-brightness adds one more layer. Walk from a bright kitchen to a dark hallway and your phone quietly drops its brightness, so the swatch you liked a minute ago now looks heavier.

A worked example: RAL 6005 and RAL 5015

Take two common colours. RAL 6005 moss green is a deep, dark green used on fences, railings, shop fronts and garden buildings. This site gives it an approximate screen value of #0F4336. RAL 5015 sky blue is a clear mid blue, listed here at about #2874B2. Both values are approximations for screens, nothing more.

Now picture looking at both on two devices.

Viewing situation	RAL 6005 moss green (#0F4336)	RAL 5015 sky blue (#2874B2)
Laptop at low brightness in a dim room	Reads as almost black, with only a hint of green at the edges of the swatch	Looks darker and a little greyer than a printed card
Laptop at normal brightness, neutral settings	A dark bottle green, close to what most charts intend	A clean mid blue
Phone at full brightness in daylight	Lifts noticeably, looks lighter and brighter green	Can look bright, almost electric, on a vivid display mode
Phone in night mode	Turns muddy, closer to olive or brown	Loses blue, drifts towards a dull teal grey

Why do they behave so differently? Moss green is dark, so its fate depends mostly on brightness and on how the screen handles the very bottom of its range. Many phone displays boost contrast and lift shadows in their default vivid mode, which helps photos and hurts dark paint colours. Sky blue sits in the middle of the scale, so brightness matters less, but its blue channel is doing most of the work. Anything that trims blue, such as a warm white point or night mode, pulls it towards green and grey.

The practical lesson is that the same two numbers can produce a dark green that looks black on one device and a blue that looks two shades too bright on another, with no error anywhere in the data. If you were choosing between 6005 and a lighter green for a fence on your phone at ten in the evening, you would be choosing between two distorted versions.

Why different charts list different hex values

Search for a RAL number across a few online charts and you will often find two or three hex values that do not agree. This confuses people, and it is easy to assume one site has made a mistake. Usually several honest choices explain the gap.

1. The starting point differs. A hex value has to come from somewhere: a measurement of a physical card with a colour instrument, published colorimetric data, or a conversion someone else already made. Different instruments, cards and lighting conditions give slightly different numbers.
2. The conversion differs. Turning a measured colour into sRGB involves choices about the reference light (paint is usually measured under a daylight standard, and screens assume their own white) and how to adapt between them. Two careful people can pick different methods and land a few steps apart.
3. Out-of-range colours get clipped differently. If a colour sits outside sRGB, there is no correct hex value, only a choice of which nearby colour to show. One chart keeps the hue and drops saturation, another keeps saturation and shifts the hue slightly.
4. Rounding and copying. Many charts copy values from older charts, sometimes with typing errors, and nobody goes back to check.

A difference of a few points in each channel rarely matters for picking a colour family. It does matter if you try to use a hex value as a specification for paint, which it is not. If you need to go the other way, from a hex value in a brand guide to the nearest RAL Classic number, the match lab will give you a starting point, but treat its answer as a shortlist to check on paper, not a final choice.

Why physical samples win

A physical sample takes the screen out of the chain. It is lit by the same light as the wall, door or railing you are going to paint, and your eye judges it in the same conditions. A few habits make samples far more useful.

• Look in daylight, ideally indirect light from a north-facing window or outdoors in the shade. Direct sun and warm bulbs both distort.
• Hold the sample against the real surroundings: the brick, the render, the timber, the neighbouring door. A colour that looks right on a white page can look wrong against red brick.
• Remember that a small chip looks darker and less intense than a large painted area. If you can, paint a sheet of card at least the size of a magazine page and look at that.
• Check the sample at two times of day. Colours shift between morning and evening light, and some pairs of paints that agree in daylight disagree under artificial light.

A printed chart is better than a screen but still a step removed, because printing inks have their own limits. A RAL Classic fan deck gives you painted or carefully produced colour strips you can carry to the paint counter, and it removes most of the guessing for the common shades. Better still, for anything large or expensive to redo, ask the supplier for a sample pot or a sprayed test panel in the actual product you will use, because gloss level and texture change how a colour reads.

What a screen is still good for

None of this makes screens useless. They are fine for narrowing a choice from two hundred colours to five, for seeing roughly how a grey sits next to a white, and for comparing colours side by side on the same device at the same settings. Comparison on one screen is far more reliable than judging a single colour in isolation, because whatever the screen does wrong, it does to both colours at once.

If you do use a screen, give it a fair chance. Turn off night mode and any automatic colour or white balance adjustment while you look. Set the brightness to a middle value and keep it there. Use the same device each time you compare. Avoid judging dark colours on a phone held at an angle, since many panels shift colour and contrast when viewed off-axis.

Then take your shortlist to paper and paint. The last decision should always be made with a physical sample in your hand, in daylight, next to the thing you are going to paint. The number tells the paint shop what you want, and the sample tells you whether you actually want it.