Drawing with the brush allows the painter more freedom of expression. Using charcoal or a pencil means sacrificing the fluidity and sweep that can be attained with the brush and a liquid medium. Any color can be used when doing this procedure because the color will be lost with the paint being on top. For myself, I would choose a color that I plan on using in my painting, that way if the lines are drawn wrong you do not have to wipe them out you can just change the color and paint it over again.