Screen Colour Test

A monitor can handle most content without anything looking wrong and still fail in specific situations: a sky gradient that breaks into stripes, a white that leans blue, or a dot that stays red no matter what is on screen. This test cycles through full-screen primary and secondary colours plus a set of smooth gradients, putting each of those defects on a large uniform surface where they have nowhere to hide.

Flat full-screen colour is the fastest way to find problems. On pure red, any pixel that fails to light that subpixel jumps out immediately; on a grey gradient, the banding that normal images disguise with texture becomes obvious; and on full-screen white, the dominant tint shows up the moment you compare it mentally to a sheet of paper. The whole sequence runs in the browser and needs nothing installed.

How to Use the Colour Test

Put the test in full screen, wipe the panel first so a speck of dust does not get mistaken for a dead pixel, and dim the room. Step through each solid colour and scan it corner to corner looking for points that do not belong: a black dot on a red field means a subpixel that never lights, while a coloured dot on a black field means one that never switches off. Then move to the gradients and check whether the transition stays continuous or breaks into visible steps. Look from close up and from a normal distance, because some banding only appears at certain viewing distances. Keep the limitations in mind: a browser cannot measure gamut or colour accuracy, so this catches obvious defects rather than certifying sRGB coverage or delta E. The image also passes through the graphics card, the operating system and the browser itself, so a badly applied colour profile can change what you see without the monitor being at fault.

Colour Coverage and What It Means

Coverage figures describe how much of a colour space a panel can reproduce. Use them to interpret what you see on screen, remembering that this tool does not measure your monitor gamut.

Why Banding and Tints Appear

Banding is a visible step in an area that should show a smooth transition. It happens when the panel lacks enough intermediate levels to render the gradient and groups several tones into the same value, so instead of a continuous ramp you get stripes divided by hard edges. It shows up mostly in skies, smoke, graduated shadows and fades to black, in other words wherever no texture is present to disguise the jump.

The most common origin is 6-bit panels with dithering, which manufacture the missing tones by alternating rapidly between two adjacent values so the eye perceives an average. The trick works remarkably well across most images, but on a wide clean gradient the eye catches the pattern and the bands emerge. Content compression, a cable or video mode that reduces chroma subsampling, and some of the monitor own image-enhancement filters all contribute as well.

Tints are a different matter. It is worth separating gamut from accuracy: gamut describes how many distinct colours a panel can reach, while accuracy describes whether the colour it shows matches the colour it was asked for. A monitor can have a huge gamut and still look green because its channels are unbalanced. If you spot a clear cast on full-screen white, in most cases it is fixed from the RGB settings in the monitor menu by lowering the dominant channel rather than raising the other two.

Tips for Reading the Test

• Clean the screen first, because most of the dead pixels people believe they find turn out to be dust.
• Inspect each solid colour up close and then from a normal distance, since small defects change visibility with range.
• Correct tints in the monitor RGB settings by lowering the dominant channel, never by maxing out the other two.
• Turn off blue-light filters and system night modes before judging any colour cast.
• Check that the video output colour range matches what the monitor expects, to avoid artificial banding.
• Retest with a different cable or port if you see odd banding, since the connection is sometimes the culprit.