In Colour Sudoku, instead of filling in the numbers 1 to 9 in each of the 3 by 3 blocks, you must enter 1 to 9 in the 9 boxes of each colour - i.e. there are nine yellow boxes, and the yellow boxes must contain the digits 1 to 9.
You find a daily puzzle on: http://www.coloursudoku.com/
