• Choose a number or a color from the top, then tap cells to place it. The selected choice is outlined in green.
• Tap a cell that already has the selected number or color to clear it.
• Placements that would repeat a number or color in a row, column or block, or reuse a number-color pair, aren't allowed.
• Numbers and colors that are part of the puzzle are fixed. Given numbers are underlined, and given colors have a small white corner.
• Turn on "Color letters" to show a letter for each color (R red, G green, K black, B blue, P purple, O orange, Y yellow, I pink, T teal).
• Show Hint points out a mistake if there is one; otherwise it highlights a cell you can fill next and explains why.
• Click New Puzzle to pick another puzzle or level. Finished puzzles are green, and partly solved ones are partly green.

Every cell gets a number and a color. Fill in the grid so that:

• each number appears once in every row, column and block (the areas inside the thick lines),
• each color appears once in every row, column and block, and
• every number and color pair appears exactly once in the whole grid. If one cell is a red 2, no other cell can be a red 2.

Some cells start with only a number, some with only a color, and some with both. The 4×4 puzzles use 4 numbers and 4 colors; the 9×9 puzzles use 9 of each.

Work on the numbers and the colors separately at first: each one is an ordinary sudoku.

The pair rule is what makes it a puzzle. When a cell has its number but not its color, check which colors are already paired with that number elsewhere; those are ruled out. The small squares on each number button show the colors that number can still go with.

Near the end, look for a pair that only fits in one cell. In a 4×4 there are only 16 pairs, so each one you place narrows the rest quickly.

Every puzzle can be solved with these steps alone, no guessing needed.