Take regular copy paper and tear into strips ... kinda tear it so it waves or rolls along, don't tear it straight.
Starting at the TOP of your cardstock, line up one of the tear sheets. Take your ink - I used "ballet blue" in classic dye - and dip your stipple brush into the pad. Then take the stipple brush, holding the torn paper in one hand .... "stipple upward" that is brush the color up from where the tear is to the top of the page. Then move the torn sheet down a level and in one direction or another (this will give you waves in different places) - and repeat - brush the color up from where the tear is, but this time stopping before the row you just made. Ink the brush as often as necessary to get good color. I did three rows of ballet blue
Next, I took bashful blue - and a new strip - and did the same thing. Three rows of bashful blue.
Clean your brush and let it dry before changing to a new color family - or use a different stipple brush. Then, I took "creamy caramel" - and a new strip - and added three rows - which pretty much took me to the bottom of the paper. Last, I took the brush and just kinda brushed around the bottom - blended in the bottom edge.
(If you look closely at the pic, I think you'll see how the paper is divided into three sections - with the darker blue being closer to the top).