Sketch pen in any colour leaves very deep and attractive lines on paper. But because the lines from a sketch pen are so deep, that?s why a sketch pen is not a good choice for colouring inside a drawing. The spreading ink will really make the drawing look very heavy. In case a figure needs to be drawn and then coloured with a sketch pen, then it is a much better idea to use the sketch pen to draw simple lines, dots and other shapes to give the impression of colouring, without actually wetting the page. Please visit us : https:/ / www.elkospens.com/ sketch-pen.html .