To easily determine coloring, x-wings and other squirmbags, you can color your Sudoku with the colors at the bottom of the interface

You can procced by drag & drop or long press on the cell

All combinations are possible

By swipping your finger across a row or column, you color the whole row or column.

The last color allows you to erase all the colors in a cell, a column or a row (including candidates)

A long press erase all colors

By selecting a color, the drag-candidates cells are modified in the color you choose. You can now use them to change the candidates colors in the sudoku

You can also color the Helps steps and your registered Sudokus.

Still by drag & drop