What does it mean when a row or column is trapped in one colour?

If every open tile in a row (or column) belongs to the same colour, that line's queen will be that colour's queen. The colour only gets one queen, so its tiles outside that line can be crossed out. It is the mirror image of a colour trapped in one line.

An example

queenalready ruled outplay herecross out nowtiles to look at

Every open tile in row 1 belongs to the lagoon colour, so that colour's queen must be in row 1. Cross out its tiles everywhere else.

Why it works

The line needs one queen, and every tile it could use is one colour. So that colour's single queen is in this line, and none of the colour's other tiles can hold it.

How to spot it

• Look at rows and columns that pass through one large colour, especially along the edge of the board.
• Look again after crossing tiles out: a row with tiles of three colours can drop to one colour quickly.
• It pays off most when the colour is big, because a lot of tiles get crossed out at once.

Related techniques

See a colour trapped in one line for the mirror image, and pairs and triples for two or three lines at once.