Play Color Sudoku Online

What is Color Sudoku?

Color Sudoku is sudoku played with nine colours instead of nine digits. Fill the 9×9 grid so that:

• every row holds each of the nine colours once;
• every column does too;
• and so does every 3×3 box.

The colours are red, blue, green, yellow, purple, orange, pink, cyan and brown, in the order of the buttons under the grid. Sudoku never adds or compares numbers, so nothing is lost in the swap: every technique that works on a classic board works here colour for colour, and Letter Sudoku, Symbol, Emoji and Shape Sudoku are the same puzzle drawn in other symbols.

How do you find where a colour goes?

One colour at a time. Pick a colour, find every dot of it already on the board, and look at a box that still needs it: each dot rules out its own row and column. When only one empty square of the box is left, the colour goes there, whatever else that square could hold on its own. That is a hidden single:

The same sweep works along a row or a column: a colour with one place left in a line goes there. And a square whose row, column and box already hold eight different colours takes the ninth. Between them, those two moves finish every Easy and Medium board on this page.

What do Hard boards add?

Locked candidates. When singles run out, put the colours each empty square can still hold in its pencil marks — the Notes button draws them as small dots — and look inside one box at a time. If a colour’s places in the box all lie in one row or column, the box’s copy of that colour is that line’s copy too, so it comes out of the rest of the line:

It works the other way round as well: a colour confined to one box within a row or column comes out of the rest of that box. Hard boards are dug so that singles and locked candidates finish them.

And Expert boards?

Naked pairs. Two squares of one row, column or box that can each hold only the same two colours will take those two colours between them, whichever way round, so no other square of that row, column or box can have either:

Expert boards are dug so that singles, locked candidates and naked pairs finish them, and they start with the fewest colours.

Were the boards on this page fair?

Not for their first twelve days. From 1 April 2026 the generator took colours out without checking anything, and 140 of 160 boards we dealt from that first version have more than one answer. From 13 April it checked every colour it took out with a full search, and we re-counted 160 of its boards with a separate counter to confirm it: each had exactly one answer. What it never checked was how a board would be solved. Each level only had a number of colours to leave, so the names meant less than they said. Expert was meant to leave 22 and managed it on 4 boards in 40, leaving a median of 25, much the same as Hard’s 26. And a solver that knows singles, locked candidates, pairs, triples and the X-Wing could not finish 26 of the 160 boards — 3 Medium, 12 Hard and 11 Expert — though the page promised that no guessing was ever needed.

The generator was rewritten in September 2026, the same fix as Letter Sudoku’s, which dealt from the same code. It now takes a colour out only while the level’s own steps still solve the board, which also proves the board has exactly one answer, and a new board appears in well under a tenth of a second at the median. The colour buttons had no names at all before; a screen reader announced nine blank buttons.

How do the four levels differ?

By how many colours are given, and by the steps a board is dug for. We dealt 40 fresh boards per level from the new generator, and 40 per level from the old one:

40 boards per level, fixed seed. Expert digs toward 22 colours as far as its steps allow and keeps the fewest of up to six tries: 22 to 25, median 23. On the new boards nothing past naked pairs was ever needed: one Hard board could not be finished without locked candidates, and three Expert boards not without pairs.

At the top the new levels are easier than the old ones, and fair all the way down. Most Hard and Expert boards now fall to singles alone, and what makes them harder is having fewer colours to start from — 26, and about 23 — against Medium’s 32. The old Hard and Expert were harder mainly because more than a quarter of their boards needed more than any level here teaches.

Which level should you play?

Start on Easy if sudoku is new to you, or on Medium if you know it with numbers. Easy gives 40 colours and Medium 32, and both fall to singles alone. The page opens on Medium.

Sweep one colour at a time: select a square that holds it and every dot of that colour lights up. Where two colours look alike to you, number them in your head the way the keys do. Hard and Expert then add the two moves above, on boards with fewer colours to start from.

What do the buttons do?

Select a square, then a colour; the page opens on Medium. Selecting a square highlights its row, its column and its box, and a wrong colour is marked the moment it goes in. Under the grid:

• Notes turns pencil marks on and off; they show as small dots. A correct colour clears itself from the notes of its row, its column and its box; a wrong one leaves the other squares’ notes alone.
• Erase clears the selected square, and pressing the same colour twice does the same.
• Undo takes back the last change to a square, though not the notes a correct colour cleared elsewhere, and not the Mistakes count.
• Hint fills one square with its answer, picked at random rather than the square you could work out next.
• Solve asks first, then fills the grid and stops the timer.
• New Game deals another board at the level you are on; the level buttons deal one at theirs.

From a keyboard: 1–9 for the colours in button order (1 red through 9 brown), the arrow keys, Backspace or Delete and Ctrl+Z. The board is saved in this browser after every move, so it is waiting when you come back.

Where to go next

The same puzzle in other pictures: Symbol Sudoku, Emoji Sudoku and Shape Sudoku.