notation in different colours on Solo

[jvangiel]

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When I play Sudoku on paper I make pencil notations that only count for the horizontal, vertical direction or only for the 3x3 grid.
I have not found any digital version of the game that allows me to do so.

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Have the possibility to give different colours to the notations. 3 should be enough: one for vertical, one for horizontal one for the block.

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On paper I distinguish by the location where I put the notations, but this might be hard to manipulate on a digital game.

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