1. Gradient background

Create a rectangular path and fill it with blue gradient.

[ Register or Signin to view external links. ]

2. Screen gradient paths

Create another path with Blue-Black gradient and select Screen Blending Mode. This will create a lighter blue gradient shade. If your colour setting is CMYK, make sure the black is full black (C,M,Y,K=100). The red arrow on the image is the direction of the gradient fill.

[ Register or Signin to view external links. ]

[ Register or Signin to view external links. ]

Another Screen gradient path.

[ Register or Signin to view external links. ]

[ Register or Signin to view external links. ]

3. Abstract wave

Take 2 white stroke paths.

[ Register or Signin to view external links. ]

4. Blend Tool

Go to Object > Blend > Blend Options, enter Specified Steps = 20. Then with the 2 strokes selected, go to Object > Blend > Make or press Ctrl+Alt+B. This will blend 2 white strokes and create an abstract wave effect. If you want to change the Blend step, you can go to Object > Blend > Blend Options or double click the Blend Tool(B) on the tool bar.

[ Register or Signin to view external links. ]

5. Change stroke color

Use Direct Selection Tool (A), select one of strokes and change it to blue stroke color. Notice how 2 strokes blend from blue to white. Isn't this cool?

[ Register or Signin to view external links. ]

6. Wild blend

Now go wild with your Pen tool, create 2 wavy strokes and blend them. Play around with the Blend step, stroke weight and color.

[ Register or Signin to view external links. ]

[ Register or Signin to view external links. ]

Repeat the steps and create the last abstract blend, from blue to purple.

[ Register or Signin to view external links. ]

Final

And your result

[ Register or Signin to view external links. ]