Simple Color Wrap
When one color contradicts itself inside a unit.
Explanation
Color conjugate pairs for one candidate. If two candidates with the same color see each other, that color would place the digit twice in a row, column, or box, so every candidate with that color can be removed.
Practice tip
After building a simple color chain, compare same-colored cells before looking outside the chain.
Example steps
- Choose one candidate and connect its strong links.
- Alternate two colors through the chain.
- If one color appears twice in a unit, remove that color from the chain.