Colouring cells
Some types of pattern can be thought about more easily by colouring particular cells. See Figure 1.
Figure 1: using candidate and cell colouring to spot patterns. Here, by colouring the 3's and then nine cells, the user has spotted a jellyfish.
Each cell menu has an option "Colour/uncolour cell" which, if selected, will change the background colour of the cell. If the cell has already been "coloured" by this process, its colour will be switched off, otherwise it will be set to the current cell colour. i.e. it is another toggling process. See Figure 2.
Set cell colour
The cell colour is set by a File menu option "Set cell colour" which produces a cascading menu of colours from which the user drags down to make a selection. The selected colour will then be used in all "Colour/uncolour cell" choices until the user changes the colour through this option.
Figure 2: using the cell menu to colour a cell.