Hey Toshi, there's both directions there you can go in, either darkening the panel lines or highlighting the centers of the panels. It gets you to the same place in the end so it's mostly just a matter of trying both and seeing which one works best for you. I've never tried the pastels though, so that's a third solution.
What seems to work for me is:
1). Paint model in base colour (whatever you want to end up with)
2). Spray a grey slightly darker than the base colour to the panel lines.
3). You can highlight the centers of panels here if you want as well. I don't do it that often.
4). Spray a couple of light misty coats of the base colour over the whole thing. The misty coats should blend everything together and kill any sharp demarcation in the different shades. Get it almost there and then carefully look the model over. It's easier to add one or two more mist coats than to go too far and end up having to paint everything over again.
5). You can then 'streak' the model with some thinned lightened base coat applied with quick streaks from front to back following what would be the air flow over the real plane. I picked this up from Lawdog though my attempts still don't look anywhere near as good as his.
Again, there's so many ways to do this, my advice would be to try them all and see which you like best.