Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
Rainbow Sudoku: Nine Colours, No Pictures at All
Rainbow Sudoku strips picture Sudoku down to its purest form: the nine tiles are simply colours — red, orange, yellow, green, blue, purple, pink, teal, and gold. There is nothing to name and nothing to decode; each colour fills exactly one cell in every row, column, and box.
The quietest board we make
Every other themed board gives you objects — dogs, rockets, pumpkins. This one gives you pure colour, which changes how solving feels: the grid reads as a pattern rather than a scene, and missing colours seem to announce themselves. Players who think visually often find it the fastest board on the site, and it is easily the calmest one to look at, which makes a slow 9x9 here feel closer to a mosaic than a maths puzzle.
Real rainbows run out at seven
The tile order follows the sky as far as it can. The 4x4 board is the first arc of the rainbow — red, orange, yellow, green — and the blue and purple complete the natural spectrum at 6x6. Then physics runs out: a real rainbow has nothing left to offer, and a 9x9 needs nine values. So pink, teal, and gold join as the extension colours, picked to sit as far from the original six as possible.
If red and green look alike to you
We put this plainly because it matters: red and green share the beginner 4x4 board, and they are exactly the pair that red-green colour vision deficiency — roughly one in twelve men — struggles to separate. The board is still fully playable: the Both display mode stamps a digit on every colour tile, turning the puzzle into position-and-number logic with the colours as decoration, and the plain Numbers view removes colour from the equation entirely. Nobody should be locked out of a puzzle by an emoji palette.
Our Color Sudoku is the straight 9x9 colour board — one size, no digit badges, pure spectrum. This page is the family version, with 4x4 and 6x6 boards and labels on demand.
Every colour in its place
One solution per puzzle, and no colour appears twice in any row, column, or box — the spectrum stays balanced. How grading, hints, and notes work is written up on the Themed Sudoku page, where you will also find the boards that put pictures back on the tiles.
Rainbow Sudoku FAQ
Rainbow Sudoku is the family version: 4x4, 6x6, and 9x9 boards, with an optional digit badge on every colour tile. Color Sudoku is our classic straight 9x9 colour board with no badges. The underlying logic is identical.
Yes. Switch the display to Both and every colour tile carries a digit label, so the puzzle works as position-and-number logic regardless of how the colours read. The plain Numbers view drops colour entirely.
Because a real rainbow only offers about seven distinguishable colours and a 9x9 Sudoku needs nine. The natural spectrum is complete by the 6x6 board; pink, teal, and gold are the extension colours reserved for the full grid.