Normal sudoku rules apply. Colour the grid using two colours, such that all cells of the same colour are orthogonally connected, and no 2x2 area is fully one colour. Outside clues give the sum of the first three digits seen from that direction but each outside clue ONLY sees digits of one colour, while digits of the other colour are completely meaningless for that clue. Which colour corresponds to each clue must be determined. (Each clue sees at least three digits of its colour.)