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. If this interests you, then you can get yourself a set of nice sketch pens from Elkos pens and get started on sketching with sketch pens.
For more information visit their website athttps://www.elkospens.com/sketch-pens.html .