Some tricks and tips will be added to the next update of the user guide.
There is one error that happens quite often to people (including me) when working with colour constraints. I want to force certain pieces or parts of pieces in certain positions. To do that I colourize the pieces and the target positions.
When I solve I observe, that the pieces are still placed all over the place. The problem is the neutral colour. It can accommodate all possible other colours. So:
You need at least 2 colours for a placement constraint
For a real placement constraint you need to use at least 2 colours. One colour on its own can be only usable for marks on the pieces, or to colourize the pieces for a nicer display.