Need to make something in a hurry? You can make great looking motion backgrounds quickly using Illustrator and simple, fast effects in AE. Subtlety is the key.
Open Illustrator and create a new 720x534 file. Illustrator does not support Pixel Aspect Ratio Correction.
Select the Rectangle Tool or press M on your
Draw a rectangle with a fill but no stroke.
Duplicate the rectangle and fill the art board with rectangles.
Change the color of the rectangles so that no two colors are next to each other. Do this by selecting a shape and clicking on a color in the swatches palette.
Select every second row of rectangles by Shift Clicking on shapes , and drag the bounding box to the left and right to elongate the selected rectangles.
With the rectangles still selected, choose Object>Arrange>Send to Back.
Save the file, and Import it into AE flattened as footage.
Drag the file to the New Composition button in the Project Window.
Select the layer and choose Effect>Channel>Minimax.
In the Effects Palette Choose: Operation Maximum, Channel>Color, Direction>Horizontal & Vertical.
Animate the Radius of this effect until satisfied.
You might also want to add an adjustment layer and try adding Boris Tritone, Colorama or Turbulent Displace.
When you are finished, choose Composition>Composition Settings and change the ratio to 720x480.
Back in the timeline, select the 720x534 layer, and press Cmd+Option+F (Ctrl+Alt+F) to scale to fit the layer.