Coloring tracks the implications of placing a candidate using two colors.
Understanding the Concept
Pick a candidate that appears exactly twice in several houses.
Color these "conjugate pairs" with two colors (e.g., green and blue).
If green is true in one cell, blue must be true in its pair.
Build chains of alternating colors across the grid.
Look for contradictions: same color seeing itself, or both colors in one house.
Can eliminate based on these contradictions.
Simple Coloring uses one digit; Multi-Coloring uses multiple digits.
Examples
Color Contradiction
If two cells of the same color see each other, that color is false. Eliminate that color everywhere.
Pro Tips
- •Start with candidates that form many conjugate pairs
- •Be systematic in coloring to avoid mistakes
- •Look for color conflicts and contradictions
- •Very visual technique - great for those who think visually
