Simple Coloring
Two-colour chaining of a single digit’s strong links to expose contradictions and eliminations.
Coloring tracks one digit through its strong links — units where the digit has exactly two candidate cells. Alternately colour those cells two colours; cells of the same colour are all on or all off together. Two rules then apply: if two same-colour cells share a unit, that colour is false; and any cell seeing both colours cannot hold the digit.
It is a clean, single-digit technique that often cracks puzzles where wings fail.
How to spot it
Pick a digit with many bi-location units. Start a chain: colour one candidate cell A, its strong-link partner B the other colour, then continue. Apply the two coloring rules to make eliminations or settle the digit entirely.
- Colour a digit’s strong-link cells alternately.
- Same colour twice in one unit ⇒ that colour is off.
- A cell seeing both colours ⇒ digit removed there.
Worked example
- Choose digit 5 and colour a strong-link chain blue/green.
- Two blue cells turn out to share a column.
- Blue cannot be the true colour (it would place 5 twice).
- Therefore every green cell holds 5.
- Place all green 5s and clear blue candidates.
Try it yourself
Tap a cell, then a number, to practise.
Frequently asked questions
- What is a strong link?
- A unit where a digit has exactly two possible cells — if one is false the other is true.
- Is coloring the same as chains?
- Coloring is a single-digit special case of chaining; forcing chains generalise it to multiple digits.
Related techniques
Practice: Simple Coloring
Put the Simple Coloring to work on a live board — free puzzles with notes, hints and four difficulty levels.
Try it on a live board