How to Find Hidden Pairs

Seven cells are open and the notes are crowded. No cell shows a single color, no color has a single place left, and no two cells match. Obvious Pairs and the singles all find nothing here, so stop looking at the cells and start looking at the colors.

Follow Red across the block: it appears in two cells, the ends of the bottom row. Now follow Orange, and it appears in exactly the same two. Two colors, two cells, and both colors must be placed. So Red and Orange will fill those two cells between them.

Those two cells now belong to Red and Orange, so anything else written in them is already wrong. Light Purple sits in one of them, Yellow and Dark Purple in the other, and none of the three can stay. Take them off. An obvious pair clears notes from the cells around it. A hidden pair clears notes inside its own two cells.

Yellow could go in two cells of this block, and one of them now belongs to Red and Orange. That leaves Yellow only one place, so Yellow must go there. A hidden pair never fills its own two cells. What it does is leave fewer places for every other color, and one of them usually ends up with a single place left.