
Coloring 

The technique of coloring requires you to understand the nature of strong connections  a connection between two candidates that are the only two in the unit. If one of the candidates is false, then the other must be true, and vice versa. To use the coloring technique, first colorin all these strong connections for a given candidate. For each strong connection, make one candidate one color, and the other candidate another color, and make sure these colors match up as strong connections linked together. After you have created a web of strong connections with these two colors, any candidate that shares a unit with both colors can be eliminated.
Consider the example on this page. A web of strong connections for the candidate 4 has been colored. Notice how every other candidate is the same color. There are only two possibilities, either all the yellows are 4's or all the oranges are 4's. Either way, the 4 highlighted in green can be eliminated.
Notice that for coloring to work, all the strong connections have to be interconnected. Connections in a different web, even of the same number, are not relevant. Because of the work involved to spot this technique, Sudoku Snake gives it a skill value of 200.






