Let's take a trip back to the Mod 60's to explore Op Art.  According to Wikipedia:

"Optical art is a method of painting concerning the interaction between illusion and picture plane, between understanding and seeing." Op art works are abstract, with many of the better known pieces made in only black and white. When the viewer looks at them, the impression is given of movement, hidden images, flashing and vibration, patterns, or alternatively, of swelling or warping."

To get a better visual idea, search for Op Art Images on the internet.

According to the Handbook for Flower Shows of the National Garden Clubs, an Op Art design is:

"1. An Abstract Creative Design having implied visual motion. Therefore it is considered a Kinetic Design.

2. Patterns and colors are arranged to force the viewer's eyes to move back and forth quickly from one dynamic area to another. This gives the illusion that the color patterns move.

3. Bold interest areas caused by the use of intense colors provide rhythm through the design.

4. Op art fabric, paper, plastics, or forms typically provide the optical illusion; therefore, it is vital that plant material and other (optional) components be organized with simplicity and strong clarity, lest the total design appear visually disturbing."

This is a good design in which to "think out of the vase".

Backgrounds, mounted on foam core, are an easy way to start.  Find a patterned poster or fabric and play off the vibrant colors presented to select structures and plant material for the foreground.  As the handbook indicates, you direct the viewer's eye through the design (rhythm) by providing resting points, or bold interest areas.  

Let your creative spirit fly with this one.  Consider using dried plant material to free you from having a point of hydration. Build your own structure from unexpected materials.  Repurpose a structure meant for another use. Explore vibrant colors and spray paint.  The possibilities with this design type are endless and the results are surprising.