You should make all areas you want to make recede or where you want to suggest depth darker than the basic surroundings. If you do not want the colours to mix, be sure to wait for the first layer to dry before applying another colour over it or up against it.
Grimas Water Make-Up (Pure) can be used around the eyes, but children often do not like it when brushes are so close to the eyes. So decide yourself how far you want to extend the colour.