So, in the process of looking up different designs for a background, I stumbled across a DIY optical design.  You are basically making your very own optical illusion with the use of three basic art tools: paper, sharpie and colored pencil.  There are only 9 simple steps to creating your own design.

Step 1: Draw 9 or more vertical lines that vary in their amount of wavyness.
Step 2: Draw a single horizontal wavy line across all of the vertical ones.
Step 3: Use a ultra-thin Sharpie to draw the curves moving upwards. up-side-down ‘U’ shape
Step 4: Using the same ultra thin Sharpie to draw the curves moving downwards. right-side-up ‘U’ shape
Step 5: Connect each vertical line with the ‘U’ curves.
Step 6: Shade each section with one color hue to be dark on the edges and lighter in the middle.
Step 7: Use an analogous or similar color and create the same gradation in the next section.
Step 8: OPTIONAL: Choose another analogous color for the same row or use the original color.
Step 9: For the next row, use a complimentary or opposite color hue.

The link below has step by step photographs to help explain how to create your own design.
My optical design turned out to be pretty interesting.  I used the favorite colors of the person whom I was making the card for and alternated them in the design.   I then used the same line pattern through out the cards but not the gradation of the colors.  *Photos of finished example coming soon*

link to original site: