Opposite
From Sudopedia, the Free Sudoku Reference Guide
Jump to navigationJump to searchCandidates are opposite when only one of them must be true, while the other must be false. They have opposite parity within a cluster.
In coloring, colors represent parity. Since there can only be two colors in a single cluster, one of them must belong to the solution, while the other does not. All candidates with the same parity are equivalent.
