A puzzle.
A palette. A pause.

Place every colour once in each row, column and box. Fixed clues cannot be changed. Select a square, then a colour.

Notes show legal possibilities. A correct placement removes its matching note from connected squares. Three incorrect placements end the challenge. Undo does not restore a lost life.

Choose 16×16 and switch to shapes. Shapes and colours are separate views of the same puzzle; solid, outline, symbol and character families are available.

The hint coach explains naked and hidden singles in stages. If it cannot find a single, it explicitly offers a solution reveal instead of claiming a logical deduction.