Simple Colors

For one digit, mark cells connected by strong links (units where the digit has exactly two candidates) and alternate two colors along the chain. Exactly one color holds the digit.

Color wrap: if two cells of the same color see each other, that color is false, so the digit is in all cells of the other color. Color trap: a cell outside the chain that sees both colors cannot be the digit.

Notation

Simple Colors Trap: 6 can be removed from r3c1.