This depends very much on the pen, the colour used and the surface affected. With the STABILO woody 3 in 1, the colours can be removed from glass, quite easily with a damp cloth. On clothing, this becomes more difficult depending on the fabric. Here first try to dab off the colour with a damp microfibre cloth until the fabric no longer gives off any colour. Then wash at the temperature specified for the fabric. It may be possible to pre-treat the stain with bile soap or special stain sprays. However, not all fabrics are suitable for this and traces may remain. Basically, the colours lilac and violet are worse to remove than others.