Easy technique
Last Possible Number: The Only Color That Fits
Also called the last possible number, or a naked single spotted without notes. In Bubble Sudoku it is an Obvious Single: Last Possible.
Every cell belongs to a row, a column, and a block. Count the different colors those three contain. When you can see eight, the ninth is the answer.
1
Count the colors around one cell
BEFORE
This empty cell belongs to the shaded row, the shaded column, and the center block. Read down the column: Red, Orange, Yellow. Read across the row: Light Green, Dark Green, Turquoise. The block adds two more: Dark Blue and Light Purple. That makes eight different colors.
2
Place the last possible color
AFTER
A cell can never repeat a color from its own row, column, or block. That rules out eight colors here, so only Dark Purple is left. Place it.
Cells being readKey cellColor tints match the color being followed
Key Insight
Full House counts one row, column, or block at a time. Last Possible counts all three around a single cell. It works best where a busy row, a busy column, and a busy block cross. When your count reaches eight, place the ninth color.
If you’re stuck on a puzzle, see what to try next, in order.