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Simple Coloring
Learn simple coloring: trace one digit through its conjugate pairs, two-color the chain, then eliminate by the color-trap and color-wrap rules.
Simple coloring (also spelled colouring) tracks a single digit through its strong links. Wherever the digit appears exactly twice in a unit, the two cells are a conjugate pair: colour one and its partner takes the opposite colour. Following these links paints a connected chain in two alternating colours.
Two rules then apply. The colour trap: any uncoloured cell that sees both colours of the chain cannot hold the digit, since one of those colours is true. The colour wrap: if two cells of the same colour ever sit in the same unit, that whole colour is false — every cell of it loses the digit, and the other colour is confirmed.
Coloring generalises the Skyscraper and kite into chains of any length, and is the bridge to full chaining logic. The example highlights a coloured chain and the eliminations its colours force.
Practise the Simple coloring
The best way to learn a technique is to use it. Play a puzzle at the level where it first appears, or drop a tricky board into the solver to watch it in action.
Frequently asked questions
What is simple coloring in Sudoku?
A single-digit technique: colour the cells of a conjugate-pair chain in two alternating colours, then eliminate the digit from cells caught by the colour-trap or colour-wrap rules.
What is the difference between a color trap and a color wrap?
A trap removes the digit from an outside cell that sees both colours. A wrap detects two same-coloured cells in one unit, proving that colour false and clearing the digit from all of them.
Is coloring the same as an X-Chain?
They overlap. Coloring uses only strong links and two colours; an X-Chain may alternate strong and weak links. Both are single-digit chaining methods.
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