How to solve simple coloring in Sudoku
Simple coloring follows a chain of two-place links for one digit, colors the cells in two colors, and uses the colors to remove candidates.
How it works
Whenever a digit has exactly two places in a unit, one of them is true. Chain such links together and color the cells alternately, say blue and green. Exactly one color holds the real digit.
If two cells of the same color see each other, that color is false, so remove the digit from all of it. If a cell sees both colors, one of them is true, so remove the digit from that cell.
How to spot it
Pick a digit that has many two-place links on the board and trace them. It is easier on paper, with two highlighter colors.
A worked example
This is a step from a real puzzle, a moment where the next move needs simple coloring.
A and B are the two colours. Struck-through digits are the ones that can be removed.
The 7s form a chain whose cells alternate between two colours; exactly one colour holds the real 7s. R9C1 and R8C2 share a colour but see each other, so that colour is wrong. Remove 7 from all of it: R1C5, R3C9, R4C4, R9C1, R5C2, R8C2, R9C7.
Where it fits in Rocksled Sudoku
Puzzles that need simple coloring are never rated below Expert. Each step of this kind adds 74 points to a puzzle’s difficulty score. When you ask for a hint that needs it, the game names the technique and shows the cells involved. See how to play for the rest of the controls.