which brand of pen did you use? i actually stand corrected. the tip i used must've been .5mm. i bought this at ebay from an auto paint supply place. it is a touch up pen with ball point. see the first pic. the main problem was not being able to control the flow, since the tip is kind of like the "white out" pens, meaning slight pressure on the ball (or squeezing the pen body) causes the paint to flow out quickly.

before that i tried with .8 felt tip paint pen from the company EDDING (German brand) and the applied paint dried too fast, so repeat strokes were impossible without smudging/scratching the outline.