Sudoku technique guide

Simple Colouring Sudoku Technique

Simple Colouring follows strong links for one candidate using two colour groups. This guide explains the idea in plain English, when to look for it, and the common mistake to avoid.

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At a glance

Difficulty

Hard

This is where Simple Colouring normally sits in a human solving path.

Family

Single-digit chain techniques

It belongs to the single-digit chain techniques group of Sudoku logic.

Main action

Usually remove candidates

Most technique moves reduce notes first. That often reveals a simpler placement afterwards.

What is Simple Colouring?

Simple Colouring follows strong links for one candidate using two colour groups.

The important thing is that this is logic, not guessing. You are using the current candidates to prove that a number must either go in one place, or cannot stay in another place.

In SudoSketch, this technique is designed to work with notes and Coach highlighting, so the key cells and removal cells can be shown clearly.

How Simple Colouring works

Focus on one candidate.
Follow strong links and colour alternating possibilities.
If one colour clashes, remove it. If a cell sees both colours, remove that candidate from the cell.

When to look for it

Look for Simple Colouring after easier moves have stopped working. First check for naked singles, hidden singles, locked candidates and simple pairs. If those do not move the puzzle forward, this technique may be worth checking.

For learning, do not try to scan for every advanced technique at once. Pick one method, understand the shape, and practise spotting that one pattern.

Common mistake

Colouring only works on strong links. Do not colour through weak or casual candidate relationships.

If you are unsure, rebuild the candidates first. Bad notes create bad logic, and Sudoku will absolutely punish you for it like a tiny spreadsheet goblin.

Simple Colouring FAQ

What is Simple Colouring in Sudoku?