first,sorry for my poor English…
as you mentioned,if you don’t want to get a “pen mark” in your drawing,
there are basicly two ways you can do~
- draw fast enough,let each stroke overlap a part with each other.
thus,you can get a “not very clear pen mark”,but still can be seem…
2.overlap you strokes again and again,until the paper suck the ink to it’s limit.
thus,you can get a “absolutely no pen marks”~ this is the most simple way~
but you 'll get a more saturate color in the end.
you can check my blog articles~一人設計學院～One Man Show Design Institute: 3.1-4 使用麥克筆的各種名門正道與邪門歪道 Variety Ways For Using Makers
the article also mention about color blending,but unfortunately it is a Chinese blog.
maybe you can get someone translate for you or try the idiot auto translate in right side of blog!!! 
there are also some other sketch lesson in it!