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Hi



What does colors have to do with sudoku? :S
Which solving technique do I need to solve the next step?

Thanks in advance!

Source of this sudoku: Stefan Heine - schwierig bis extrem 1 - p.129)

There is a whole family of solving techniques called "coloring" in Sudoku. See for example the Sudopedia entry. I suspect they are referring to simple coloring in your example.

In that specific case, a candidate '6' is in each coloured cell and is in bi-value in one row, column or box.

All green or all cyan are true.

The cyan can not be true due to conflicts, so '6' green is true.

You can do the same with chains, but this is a way to expand the chains