Coloring

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Coloring

What It Is

Coloring marks one digit’s strong links in two alternating colors. If same-colored candidates clash in a unit, that color is false; if a cell sees both colors, it cannot hold the digit. Multi-coloring extends to separate chains.

When to Use

Advanced stage when a digit has several conjugate pairs; after other patterns fail to pin it down.

How to Apply (Step-by-Step)

  1. Pick a digit and find conjugate pairs (strong links) for it.
  2. Color one link’s ends blue/pink; alternate colors along each strong-link chain.
  3. Color wraps: same-colored conflict in a unit makes that color false; opposite color true.
  4. Color traps: a cell seeing both colors cannot hold the digit; eliminate it.
  5. For multi-coloring, color disjoint chains with new pairs and look for interactions.

If two blue 4s end up in the same column, blue is false and all pink 4s are real; if a cell sees one blue 4 and one pink 4, remove 4 from that cell.

See also

Scanning / Cross-Hatching Single Candidate (Naked Single) Single Position (Hidden Single) Naked Pairs / Triples / Quads Hidden Pairs / Triples / Quads Pointing Pairs / Triples (Locked Candidates Type 1) Box–Line Reduction (Locked Candidates Type 2) X-Wing Swordfish Jellyfish XY-Wing XYZ-Wing W-Wing Alternating Inference Chains (AICs) Forcing Chains / Forcing Nets Nishio Coloring Multi-Coloring Uniqueness Techniques (Unique Rectangle etc.) Fish Variants (Finned X-Wing, Sashimi etc.) ALS Techniques (ALS-XZ, ALS Chains) Sue de Coq Pattern Overlay / Template Method
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