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. Don't work too dry, but do not use too much water.
When working with Water Make-up preferably use separate brushes for light and dark colours.
Hint: Regularly change the water you rinse your brushes in and preferably work with two water bowls: one for light and one for dark shades.
