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.