Colour by number for iPhone
Mandalas, rose windows and geometric patterns, drawn to be filled rather than to be finished quickly. Twelve colours a picture, a magnifier for the tight spots, and no penalty at all for tapping the wrong place.
iPhone · free · no ads, no account, works in airplane mode
Tap a region that does not belong to the colour you have selected and the app does nothing at all. It does not fill it in the wrong colour, it does not deduct anything, it does not flash a warning. There is nothing to undo because nothing happened, which is why there is no undo button and no eraser. The whole design assumption is that you are doing this to relax, and a mechanic that punishes an imprecise thumb is working against that.
Press and hold and a loupe lifts off the canvas at 2.4× with a crosshair at its centre, so you can see the region under your thumb instead of guessing at it. Let go and it fills what the crosshair was on. This is the part of colour-by-number that usually forces you to pinch-zoom in and back out for every small piece.
Even with a magnifier, a fingertip covers many regions at once. So a tap is not read as a single pixel: the app takes a histogram of every region id inside a small circle around the touch and picks the most common one that is still unfilled. The circle is about fourteen image pixels wide when the picture is fitted to the screen, and shrinks as you zoom in, so precision follows the zoom without you having to be precise.
Choose a number and every unfilled region of that colour is highlighted across the whole picture at once. Three highlight styles are available — a solid grey, a checkerboard, and a pulsing outline tint — because which one reads best depends on the artwork and on your eyes. Finish a colour and the app moves to the next unfinished one for you.
The tedious part of a large picture is the last few regions of a colour, scattered somewhere you have not looked. Next pans the camera to one of them. It is the difference between a picture that ends and a picture you abandon at 96%.
Mandalas, peony and vine medallions, damask panels, rose windows and Islamic star geometry. The source art is generated with strict symmetry and then processed into regions, which is why the patterns hold together at the level of a single petal rather than dissolving into speckle. Nothing here is a cartoon.
Progress is stored per picture as one byte per region, written locally as you go. Close the app mid-picture, come back next week, and the canvas is the way you left it. Finished pictures collect in My Art, where you can share one or start it over from blank.
The picture is drawn by a GPU shader from two images: a map of which region each pixel belongs to, and a tiny palette strip. Filling a region changes one byte in that strip. The million-pixel region map is never touched again after it loads, which is why a fill is instant on the oldest phone the app supports and why the battery does not notice.
A colour-by-number picture is not a drawing with numbers on it. It is two images and a list, and this is how they fit together.
Two details this depends on: the id map has to be sampled with nearest-neighbour filtering, or interpolation between neighbouring pixels invents region ids that do not exist; and it has to be uploaded with no colour-space tag, or a colour conversion quietly corrupts the numbers.
Nothing. Every picture ships inside the app, so the first launch works with the phone in airplane mode and nothing is ever fetched.
There is no account and no sign-in. The app keeps an anonymous identifier generated on the device, purely so its own local database has something to key rows on. It is never sent anywhere, because there is nowhere for it to be sent.
Your progress, your finished pictures and your settings live in a local database and are deleted with the app. No analytics SDK, no advertising SDK, no crash telemetry with your artwork in it.
Sharing a finished picture uses the standard iOS share sheet, so the image goes wherever you send it and nowhere else.
Free, and version 1 has no in-app purchases and no advertising of any kind — not a banner, not an interstitial, not a video for a hint.
If that ever changes, the line that will not move is the one in the app’s own contract: nothing on the canvas. No ad has ever been placed over the artwork and none will be.
Nothing. The tap is ignored. It cannot be filled with the wrong colour, so there is nothing to correct and no undo needed.
Press and hold instead of tapping. A magnifier appears with a crosshair, you move to the region you want, and it fills when you lift. Zooming in also shrinks the tap-correction radius, so precision improves as you zoom.
No. Everything is in the app already and the app makes no network requests.
Yes. Finished pictures sit in My Art with a paint-again option that clears them back to blank.
They appear once you are zoomed in far enough to read them — below that the picture would be unreadable under a layer of digits. When you are zoomed out, use the colour highlight instead: it shows you every region of the selected colour at once.
It is not designed for them. The artwork is mandalas, rose windows and geometric pattern work aimed at adults, and the app collects nothing from anybody.