Some types of pattern can be thought about more easily by colouring particular cells. See Figure 1.
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.
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.