How to play Color Sudoku

Play Color Sudoku

The rules

The grid has 6×6 cells, split into six boxes of 2 rows by 3 columns. There are six symbols, each a color with its own shape: a red circle, a blue square, a green triangle, an orange diamond, a purple star and a sky-blue hexagon. Some cells already hold a shape: these are the givens. Fill every empty cell so that:

• every row holds each of the six shapes exactly once;
• every column holds each of the six shapes exactly once;
• every 2×3 box holds each of the six shapes exactly once.

Every puzzle has exactly one solution, and logic alone is enough to reach it.

How to play here

• Select a cell: click it, or use the arrow keys.
• Place a shape: keys 1–6, or the shape buttons below the grid. The small number on each button is its key.
• Notes (small candidates): press N or the Notes button. In notes mode, a shape you choose is recorded as a small candidate instead of an answer. Shift with a number key also adds a note.
• Erase: Delete, Backspace or 0, or the Erase button.
• Undo and redo: Ctrl+Z and Ctrl+Y (on a Mac: ⌘Z and ⌘⇧Z).
• Hint: each press of Hint tells you more: first where to look, then which technique works there, and finally the shape itself. If there is a mistake on the board, the hint shows you where.

A shape that repeats in its row, column or box is marked with stripes and a ring. Your progress is saved automatically in your browser.

Difficulty levels

The level isn’t set by the number of givens. It’s set by the hardest technique the puzzle requires:

Easy puzzles have at least 14 givens.

Techniques

Full house

A row, column or box has only one empty cell. It takes the one shape that is missing.

Hidden single in a box

Take one shape and one box: if the shape can go in only one cell of that box, place it there.

Hidden single in a row or column

The same scan along a row or column. Lines are harder to scan than boxes, so this is a medium technique.

Naked single

A cell sees five different shapes in its row, column and box, so only the sixth shape fits.

Box and line

If, inside a box, a shape can only go in cells of one row, it must be on that row within the box, so remove it from the rest of that row. It also works the other way round, and with columns.

Naked and hidden pairs

Two cells of a unit that can only hold the same two shapes take both of them: remove those shapes from the rest of the unit. If two shapes fit only the same two cells, those cells hold nothing else.

X-Wing

If a shape fits exactly two cells in each of two rows, and those cells are in the same two columns, remove that shape from the rest of the two columns.

XY-Wing

Three cells with two options each: a pivot {X,Y} and wings {X,Z} and {Y,Z} that see the pivot. One of the wings is Z, so any cell that sees both wings can’t be Z.

Tips

1. Scan shape by shape: pick a shape that is already on the board often and look for the boxes where it is missing.
2. Start with the boxes, then the rows and columns.
3. Write notes only when scanning gets stuck.