---
title: "Simple Coloring: Sudoku Technique #18 | Sudoku Flow"
description: "Simple Coloring: Coloring a chain of strong links splits it into two colors, one true and one false. An uncolored cell seeing both colors loses that…"
url: https://sudokuflow.com/lessons/simpleColoring/
language: en
---

[Sudoku technique lessons](https://sudokuflow.com/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

1. 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.
2. One color must be true, so we can remove the candidate 4 from any uncolored cell that sees both colors .

[Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/simple-coloring.html)

In our app, when this technique is the next step, the hint names it and shows you why, step by step. No ads, free to download.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_cta&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dcta%26utm_campaign%3Dlesson)

## 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.

Simple Coloring practice board:

```text
9  6  .  | .  3  .  | .  .  5
.  .  4  | 9* .  .  | .  .  .
.  1  .  | 2  .  .  | 9  .  .
---------+----------+---------
2* .  7  | 6* 8* 4  | .  .  .
6* 5  .  | 1  7* 2  | .  .  .
4* 8  1* | 3* 9  5  | 2  6* 7
---------+----------+---------
3  .  .  | .  .  .  | .  .  .
1  4* .  | 5  6  9  | 7* 3  .
.  .  .  | .  .  3* | .  4  9
```
Digits marked * were filled in by a player; the others were printed with the puzzle.

![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png)

## 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.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite)

Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.