by Greyryder
I've done both the light colored drybrush over a darker base, and the wash over the light base. I preffer the wash technique for light faded denim, and the drybrushing for darker denim, with just a little wear on it.
BTW, best old faded denim color I've found is Model Master acryl RAF Sky Type. It's pretty pale, but not a pure blue. It's got a very slight tan-ish cast to it, that really reminds me of old denim.