Simple Colouring practice sheets

The technique that rewards patience, not eyesight

Most patterns are found by looking at the whole grid and waiting for a shape to jump out. Colouring does not work that way. You pick one digit, refuse to look at anything else, and follow it until the board has nothing left to say.

That makes it the easiest advanced technique to practise alone, and the hardest to practise casually. It needs no flashes of insight — it needs you to keep a promise to one digit for three minutes.

It is also the cheapest possible introduction to chain reasoning. XY-Chain walks a line of two-candidate cells; colouring walks a line of two-spot units. Same alternation, easier object to see.

Doing it on paper

1. Choose a thin digit. Sweep the grid and count, for each digit, how many units have exactly two open spots for it. The digit with the most two-spot units is the one to colour. Usually it is a digit that already appears three or four times.
2. Mark the joins lightly. Draw a small dot or a faint line between the two cells of each two-spot unit. Pencil, not pen — you will erase these.
3. Start at an end and alternate. Any cell with only one join is an end. Shade it one way, shade its neighbour the other way, and keep flipping as you follow the chain.
4. Stop before loops. If the chain comes back to where it started, it is a loop — a four-cell loop is an X-Wing, and the X-Wing sheet is the place for it. Loops are not wrong, they are just already covered.
5. Check the cells you did not shade. Any cell holding the digit that can see a member of each shade loses it. The victim is almost always outside the chain.

If nothing turns up, check the rarer rule before moving on: two cells of the same shade that can see each other make that entire shade false, and the digit leaves every cell painted that shade.

What the grader guarantees

Every puzzle needs at least one colouring chain. Nothing asks for a technique more than one tier above, so the hardest extra step you can meet is around XY-Wing or a unique rectangle — and that is the honest shape of the ladder, not a defect. A board that needs only colouring tends to be a board you can finish by eye.

The filter never relaxes to fill a sheet. If one comes up short, press New set.

Printing it

Scale 100% — "fit to page" thins the grid lines, and this technique is read off thin marks.

Candidate marks are worth having on the first pass, because step 1 is counting spots and counting is unreliable from working memory. Once you can find the two-spot units by scanning, print a second copy without marks and see whether the chain still appears.

Related practice

The full guide to Simple Colouring works a real board cell by cell, including the second rule and the reason a four-cell loop counts as an X-Wing rather than a colouring.

Other sheets: X-Wing, skyscraper, XY-Chain, W-Wing.