1-9 must be placed in each row, column and marked region. The clues outside the grid indicate the sums of the contiguous runs of cells in that row or column that must be shaded black for black clues and gray for blue clues. If a clue is red, then both colors must be present in the row or column. There must be an unshaded cell between runs of the same color, though there is no need between runs of differing colors.