When we talk about color value, it is the lightness of a color , relative to another. Value always is a comparison . Take yellow, for example--it looks light compared to navy, but dark compared to white. White next to yellow will be low contrast; navy next to yellow will be high contrast.
The contrast of light and dark helps a design "pop". That's probably what the judges thought your quilt was lacking.
Here's a video I found that does a good job explaining value with crayons and fabric:
https://www.bing.com/videos/search?q...F966&FORM=VIRE