Sudoku solving technique · Expert
Simple Coloring
Following one digit through strong links in two colors.
What is Simple Coloring?
Simple Coloring follows one candidate through strong links: rows, columns, or blocks where it appears in exactly two cells, so one of the two must hold it. Linked cells get alternating colors, and exactly one color is right. If two cells of the same color see each other, that color is wrong, and the candidate is removed from all its cells. An uncolored cell that sees both colors loses the candidate too.
How to spot Simple Coloring
Pick a digit and look for units where it appears in only two cells. Join those pairs into a chain and color the cells alternately in two colors. Exactly one color is right. If two cells of the same color see each other, that color is wrong; if an uncolored cell sees both colors, it loses the digit.
- Difficulty
- In Sudoku Pro, this technique belongs to the Expert level.
- Learning path
- Technique 18 of 20 on the learning path
An example from the app
| Empty | Empty | Given 3 | Given 1 | Empty | Empty |
| Given 6 | Empty | Empty | Empty | Empty | Given 4 |
| Given 3 | Empty | Empty | Empty | Pattern (purple). Candidates 1, 2, 6 | Given 5 |
| Pattern (purple). Candidates 1, 2 | Given 6 | Given 5 | Empty | Given 4 | Second pattern group (hatched). Candidates 1, 2, 3 |
| Given 5 | Empty | Empty | Empty | Empty | Empty |
| Second pattern group (hatched). Candidates 1, 2, 4 | Given 3 | Given 6 | Empty | Affected cell (orange). Candidates 2, 5. Eliminated 1 | Empty |
Small digits are candidates. Crossed-out digits can be removed in this step.
- Pattern (purple)
- Second pattern group (hatched)
- Affected cell (orange)