Sudoku FlowSudoku technique lessons / Simple Coloring
Lesson 18
Simple Coloring
The rule
Coloring a chain of strong links splits it into two colors, one true and one false. An uncolored cell seeing both colors loses that candidate, and if two cells of one color see each other, that color is false.
Step by step
- Building a chain of conjugate pairs (strong links) for 4: each link joins a cell and a cell that are the only two cells for 4 in one row, column, or box.
- One color must be true, so we can remove the candidate 4 from any uncolored cell that sees both colors .
Try it on more boards
Each board is a real puzzle from our app, at a moment where Simple Coloring applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.
Want more boards like this?
We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.
Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.