Intensity? What's that? Simple put it's the saturation of color of the fabric. A high intensity fabric will be filled with bright colors, with an obvious depth of saturation--rich and deep. A medium intensity is what most quilters select because it's what most fabric producers sell. It's safe and doesn't need much risk to go with medium intensity choices. Low intensity, usually tone on tones or muted colors against low saturation colors--such as a light grey design on a cream colored background--are also safe, easy to use fabric choices.
So how do you put the 'va va voom' into a quilt? How about taking risks and using some high intensity choices in place of some of your medium intensity fabrics. Add some low intensity fabrics as well for a high contrast of your design. That "pop" of color here and there will bring a design to a higher wow factor and add interest to your work. This very interest may grab attention to the beauty of your work and make someone want to gaze longer at your work of art.
This is not a safe way to quilt. It takes bravery and a desire to move beyond where you have been before. Many of the modern and contemporary designs use this very technique to distinguish the work from tradition quilts. It is the depth and dimension that adds interest and makes the quilt more Warm colors will advance an image while cool colors tend to make them recede. Deep, high intensity colors make images appear close while low intensity colors tend to make things look farther away.
Take a chance and advance your quilt making skills. Try a little change in intensity to give your next quilt top a big "POW" that makes you smile when you look at it and makes others feel compelled to keep looking. You might be surprised at what you discover in your own design aesthetic.