Simple Sudoku suggests *7* can be excluded based on colors. I've used "a" and "b" as the representation of different colors. However, looking at the problem, I thought with colors, that you couldn't make a decision on which one was true or false until you had two of the same color in one box? Can someone explain how this one works?

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` *--------------------------------------------------*`

| | | 7 |

| 7a | 7b | |

| 7b | 7a | |

|----------------+----------------+----------------|

| 7b | *7* 7 | |

| 7a | 7 7 | |

| | | 7 |

|----------------+----------------+----------------|

| | | 7 |

| 7 | | |

| | 7 | |

*--------------------------------------------------*