Red White And Blue
Red, White And Blue is one of the friendlier of the tough mental workouts. The puzzle is played on a 6x6 grid, and each square is to be marked as red, white or blue in such a way that every row, column and long diagonal contains two squares of each colour. For each row and column, one clue to the layout is provided, taking forms like "Both reds are further left than both blues" or "The blues are not adjacent to the whites".
With only three possible options for each square, working through the clues one by one and using a simple process of elimination is usually enough to suggest the correct logical path through the puzzle.