I did it the same way John said, but since I'm new at this I had to do it over and over, until the desired finish was achieved.
I hand sand the flats up to 600 grit, and then I took the bevel up to the blue scotch brite belt. Just as you've noticed the scotch brite belt leaves a trail on the flats, but it doesn't take much effort to clean up the flats since they've already been taken to 600 grit. I had to go back and forth from the scotch brite belt on the bevel, to the 600 grit on the flats until I got the crisp sharp lines I was looking for.
There is no easy way to achieve the results one is looking for, only hours of hand finishing will get you there. I hope to some day get quicker at this knife making stuff. If there is one thing I've learned about the process, it's to take each step to completion. The better you grind the bevel, and the more time you spend on making sure your flats are truly flat; the better the grind line where the bevel meets the flats will be, and the easier it will be to final finish. I'm just learning this lesson myself, I'm only on knife #3 so far.
Don