Why colours look different when you zoom in
A small region really is being blended with its own outline before it reaches your eye, and your visual system shifts a colour’s apparent value depending on what surrounds it. Both effects vanish when you zoom.
You fill a small petal, decide the colour looks wrong, zoom in to check, and it is a different colour from the one you were just looking at. Nothing changed in the file. Two separate things are happening, one in the display pipeline and one in your visual system, and both of them are worth understanding because both have practical consequences.
The display side: a small region is literally blended
When a picture is fitted to a phone screen, the artwork is larger than the space available. The long edge of the canvas is 1536 image pixels, and the screen area it is drawn into is generally smaller than that, so one screen pixel ends up representing more than one image pixel.
What the display shows you for that screen pixel is an average of what fell under it. If a region is four image pixels across and is bordered on both sides by a near-black outline, then the screen pixels covering it are averaging that region’s colour together with the outline colour. The result on screen is genuinely darker and less saturated than the colour in the palette. You are not misjudging it — you are looking at a mixture.
Zooming in reverses this. Once the region occupies many screen pixels, most of them contain only the region’s own colour, and the outline contributes only along the actual boundary. The colour you now see is the palette colour. That is why the zoomed view is the one to trust.
The effect is strongest exactly where it is most annoying: on thin regions, on the smallest areas of a dense mandala, and on light colours next to dark outlines, where the proportional shift is largest.
The perceptual side: simultaneous contrast
The second effect is in you rather than in the screen, and it is larger than most people expect.
Human vision does not report absolute values. It reports differences, computing a patch’s lightness largely relative to what surrounds it. The same physical colour looks lighter against a dark surround and darker against a light one. This is simultaneous contrast, and it is not an illusion in the sense of a trick — it is how the system works, and it is doing something useful, since it keeps a surface looking like the same surface under changing light.
For colouring, this means a small region surrounded on all sides by dark outline is being judged against a dark surround, and reads lighter than the same colour filling a large open area — or, when the outline dominates the averaged pixels, darker. Which way it goes depends on the ratio of outline to interior, which is exactly what changes when you zoom.
It also means a colour looks different depending on which colours you have already filled around it. Fill the neighbouring regions in a pale shade and the region you were happy with an hour ago now looks too dark. Nothing about it changed.
Things outside the picture that change it too
Automatic brightness
Phones adjust display brightness continuously in response to ambient light, and the adjustment is gradual enough that you rarely notice it happening. If you move from a window to a sofa, the entire screen slowly gets dimmer, and every colour on it changes with it. You will attribute the change to the region you just filled.
Colour-temperature adaptation
Many devices also shift the white point of the display to match the colour of the surrounding light — the feature Apple calls True Tone, with equivalents elsewhere. Under warm indoor light, the whole screen goes warmer. This is designed to make the screen look like a piece of paper in the room, and it succeeds, which means the colours on it are no longer the colours in the file.
If you are trying to judge a colour precisely, this feature is working against you. It is worth knowing it exists before concluding that something is wrong with the artwork.
Dark mode
Switching between light and dark theme changes the surround of the entire canvas, and by simultaneous contrast that changes how every colour in the picture reads. The same picture genuinely looks different in the two themes. Neither is wrong; they are two surrounds. If you are comparing colours, do it in one theme and stay there.
Viewing angle
On LCD panels, colour and contrast shift with the angle you view them from, sometimes considerably. A phone flat on a table and viewed from a chair is being seen at a steep angle. Tilting the device towards your face is a real change to what you see, and it is the cheapest thing on this page to test.
Why the id map is not affected by any of this
A useful detail for understanding why the app never gets confused even though your eye does. Underneath the artwork there is a second image whose pixel values are region numbers rather than colours — it is what makes an instant fill possible.
That map is sampled with nearest-neighbour filtering and no mipmaps, so it is never averaged between neighbouring pixels the way the visible artwork is. Interpolating between region 40 and region 41 would produce region 40.5, which rounds to a region that may exist somewhere else entirely in the picture, so the smoothing that helps your eye would be catastrophic there.
It is also uploaded with no colour-space tag, because a colour conversion applied to numbers changes the numbers. Every brightness and white-point adjustment described above happens to what you see, and none of it happens to what the app reads.
On the authoring side, the source plates are drawn with no antialiasing at all, so that region boundaries quantise cleanly instead of producing a soft fringe of ambiguous pixels. The visual softening you perceive at fit scale comes from the display averaging, not from the artwork.
Practical advice
- Judge a colour zoomed in. At fit scale on small regions you are looking at a blend of the colour and its outline, not the colour. The zoom range runs from fit to twelve times fit; you rarely need much to escape the averaging.
- Judge it against its finished neighbours, not in isolation. Simultaneous contrast means the surrounding colours are part of what you are seeing, so a colour judged alone will surprise you once the picture fills in.
- Keep the room light steady while you work. Moving between light conditions changes the screen twice over, through brightness and through white point.
- Pick one theme for a session. Switching between light and dark mid-picture changes the surround of everything.
- Tilt the device towards you if the colours look flat, particularly on an LCD.
- Do not chase a match between a phone and a printed reference. Two displays will not agree with each other, and no display agrees with ink. That is a property of the media, not a fault you can adjust away.
The short version
At fit scale, small regions are being averaged with their outlines by the display, and your visual system is judging them against whatever surrounds them. Zooming removes the first effect and reduces the second. If a colour looks wrong, zoom before you conclude anything — most of the time the colour is fine and the view was the problem.
Frequently asked questions
Why does a small region look darker than the same colour in a large region?
Two reasons at once. At fit scale one screen pixel can average several image pixels, so a small region bordered by dark outlines is genuinely being mixed with those outlines before it reaches your eye. On top of that, your visual system judges a patch relative to its surround, so a colour boxed in by dark lines reads differently from the same colour in an open area.
Does zooming in change the colours?
It changes what reaches your eye, not the file. Zoomed in, most screen pixels covering a region contain only that region’s colour rather than a blend with its outline, so the zoomed view is the accurate one.
Why does the whole picture look different at different times of day?
Automatic brightness and colour-temperature adaptation such as True Tone adjust the entire display in response to the light in the room, gradually enough that you rarely notice. The screen genuinely is showing different colours, and it is not the picture that changed.
Does dark mode change how the colours look?
Yes, because it changes the surround of the whole canvas, and colours are judged relative to their surround. Neither theme is more correct; just keep to one while you are comparing colours.
Why do the colours not match my printer?
Displays emit light and ink reflects it, and no two displays agree with each other either. Matching a screen to print is a property of the media rather than something you can adjust away in a colouring app.
Try it on a real canvas
Numbrush is colour by number for adults: mandalas, rose windows and geometric pattern work, twelve colours a picture, a magnifier for the tight spots, and a wrong tap that costs you nothing. Free, offline, no ads and no account.