Color Sudoku rules preserve the complete logic of a classic 9x9 Sudoku while changing only how the nine tokens are presented to the eye and to assistive technology. Every value from 1 through 9 is shown as a colored swatch, an English color name, a geometric or typographic symbol, and the digit itself, and the constraint underneath is unchanged: fill every open cell so that each of the nine rows, nine columns, and nine bold 3x3 boxes contains every token identity exactly once. Five fixed boards expose nine editable cells each and lock the remaining seventy-two as read-only givens, and each board has a single proven solution verified by an independent backtracking solver that does not look at the production code. Choose Check grid after the nine open cells are filled, and a valid board awards 200 points and opens the next fixture; clearing all five produces an exact 1,000-point run on the Color Sudoku board.
The Nine Tokens and Their Redundant Labels
Color Sudoku uses nine identities, stored internally as the integers 1 through 9, and each identity is paired with three additional presentation fields: a unique color swatch, an English color name, and a geometric or typographic symbol. The redundancy matters because hue is never the only cue. A player who cannot distinguish a particular color can still rely on the number, the spelled name, the symbol, the grid position, and the screen-reader description attached to every cell and palette token. Token 1 carries the Crimson swatch and a circle; token 2 carries the Amber swatch and a triangle; the remaining palette continues through Gold, Green, Teal, Blue, Indigo, Violet, and Rose, each with its own swatch and its own symbol.
| Token ID | Color name | Symbol |
|---|---|---|
| 1 | Crimson | Circle |
| 2 | Amber | Triangle |
| 3 | Gold | Geometric or typographic symbol |
| 4 | Green | Geometric or typographic symbol |
| 5 | Teal | Geometric or typographic symbol |
| 6 | Blue | Geometric or typographic symbol |
| 7 | Indigo | Geometric or typographic symbol |
| 8 | Violet | Geometric or typographic symbol |
| 9 | Rose | Geometric or typographic symbol |
Because the nine identities are stored as integers rather than as raw colors, the palette is a representation layer, not a new mathematical rule. Nikoli's official rules page defines the underlying one-through-nine constraint; Color Sudoku simply labels each integer with redundant accessible cues so the same constraint can be solved without relying on color perception.
The Three Constraints: Rows, Columns, and Boxes
Every playable Color Sudoku board is a 9x9 grid with 81 cells, divided into nine rows, nine columns, and nine bold 3x3 boxes. The single constraint that governs the game is the standard Sudoku constraint: each of these twenty-seven containers must contain every token identity from 1 through 9 exactly once. No other rule applies. Color groupings do not form additional regions, color clues do not replace the row-and-column-and-box logic, and no two cells sharing a swatch may share a row, a column, or a box unless their token identities are different.
Givens are read-only cells that already display a token identity at the start of a board. Clicking a given changes which cell is selected for orientation, but it never changes the cell's stored value, so a given cannot be edited, cleared, or overwritten through any input path. The remaining cells, exactly nine per board, are the only places where the player may place a new token identity. This keeps the logical difficulty of each fixture easy to learn without weakening any row, column, or box constraint.
How to Play by the Rules
- Open the Color Sudoku board and read the fixed givens on the 9x9 grid; note that seventy-two cells are locked and nine are open.
- Select any open cell by clicking, tapping, or moving to it with the arrow keys.
- Choose a palette token either by clicking the swatch or by pressing the matching number key from 1 through 9.
- Verify the placement using any cue that is not just hue: the digit, the English color name, the symbol, the grid coordinate, or the screen-reader description.
- Clear an editable cell with Backspace or Delete if a token needs to be reconsidered; givens cannot be cleared.
- Repeat for the remaining eight open cells until each row, column, and 3x3 box holds all nine token identities exactly once.
- Press Enter or choose Check grid; the board validates rows, columns, and boxes directly.
- On a valid board, collect 200 points and advance to the next fixed fixture automatically.
- Clear all five boards in sequence for an exact 1,000-point run.
The Strict Validation Rules
Check grid is deliberately strict, and every check resolves to one of three outcomes rather than to a partial credit. An incomplete board, meaning a board with at least one open cell still empty, is an atomic no-op: it does not consume an error, does not change the score, and does not manufacture a result. A completed board is accepted only by directly validating all nine rows, all nine columns, and all nine 3x3 boxes; the runtime does not compare the player's entries with a hidden answer string, so a correct fill is judged on real Sudoku logic rather than on a stored key.
When a completed board is fully invalid, the run produces an error signature from the nine editable values, the level, and the fixed fixture. Pressing Check grid on the identical wrong assignment again is deduplicated, so a single mistake does not multiply into several. A second different invalid completed assignment, however, closes the run until Restart. This keeps errors reachable and testable without punishing repeated taps on the same mistake, but it does cap how many unique full-board errors a player can sign in one session.
The Five Fixed Boards and Their Uniqueness Proof
Color Sudoku ships with exactly five fixed 9x9 boards, and the same legal completed grid backs all five. The differences live in the seventy-two givens, not in the answer; each board uses a different set of givens drawn from the same completed grid, so any solution to one board is also the underlying answer to the others, even though the visible clues look distinct.
| Board name | Role | Uniqueness |
|---|---|---|
| Spectrum Diagonal | First fixed fixture | One proven solution |
| Reverse Prism | Second fixture | One proven solution |
| Double Step | Third fixture | One proven solution |
| Offset Beam | Fourth fixture | One proven solution |
| Five-Step Hue | Fifth and final fixture | One proven solution |
Uniqueness is not assumed. A separate MRV backtracking oracle receives only each literal 81-cell puzzle, builds candidates from row, column, and box exclusions, and counts solutions up to two. Every board returns exactly one solution, and the oracle does not import the production solution array or call the runtime validity function, so the uniqueness proof is independent from gameplay code. Sharing a completion does not make uniqueness an assumption; the proof lives in the oracle, not in the post.
Scoring Rules: 200 Points per Board, 1,000 Total
Every verified board awards exactly 200 points and immediately opens the next fixed fixture, with no partial credit for partial correctness. The score only changes through verified valid completions; the score does not change for incomplete checks, repeated identical invalid checks, or color palette clicks. Completing all five boards in sequence produces an exact 1,000-point run: 5 boards x 200 points = 1,000 points, with no bonus and no penalty. The score is reset on Restart, alongside the first puzzle, zero error signatures, and the original selection.
Keyboard, Pointer, and Accessibility Rules
Pointer and touch players can select any grid cell and choose any palette token. Every grid cell and every palette or action button has a minimum target size of 44 pixels, and on a narrow screen the board uses contained horizontal scrolling rather than shrinking tap targets below that threshold, so the rules remain visual without ever falling below accessible touch dimensions.
Keyboard players move with the arrow keys, enter colors with 1 through 9, clear an editable cell with Backspace or Delete, and press Enter to check. Both input paths call the same reducer and enforce the same immutable-given, range, conflict, scoring, and terminal rules, so a board completed by mouse and a board completed by keyboard produce the same score. Visible conflict highlighting is supplemental; the selected cell, the stored numeric identity, the English label, the symbol, and the ARIA description remain available without relying on a red-versus-green signal.
Terminal States, Error Caps, and Restart
Completion is a terminal state, and deadlock, reached after a second unique invalid completed assignment, is also terminal. Once a run is terminal, extra palette clicks, arrow keys, checks, clears, and cell selections cannot alter the final record, so the recorded score, the recorded error signatures, and the recorded board position remain stable. The optional GameShell shared with other tools provides local best-score storage, the double-Escape boss screen, and a Restart control that restores the first puzzle, zeroes the score, clears every error signature, and returns the cursor to its original selection.
Because no puzzle response leaves the browser and no external gameplay endpoint is called, the full rules engine runs in the player's own tab. No account is required, no external asset is loaded, and the puzzle data, the given patterns, the palette mapping, and the validation logic are bundled in the page. The nine-token walkthrough guide covers the same rule set from a different starting point and may help readers who prefer a per-board example.
Related reading: Counting Blocks Puzzle Rules: Scores, Layers, and Errors.