The Color Trap is based on the analysis of one group of conjugate pairs. In the sudoku diagram below, we have a group marked for the digit 7. Either the light yellow cells will be 7 or the dark yellow cells will be 7. Thus, from the cells that "see" both types of cells simultaneously, we can eliminate the digit 7. In our case, we can eliminate the digit 7 from R2C1 and R3C4 because either R2C6 or R3C3 will get the digit 7. After this elimination, the digit 8 can be placed in R2C1.