Hope you don't mind that I used your photo to try and get you a black and white photo.
I used to make a lot of watercolor quilts and what helped me was to sort my fabrics into 5 piles - light, light/medium, medium, medium/dark, dark. I took out all the lightest fabrics first, then the darkest. Of the fabrics left, I again took out the lightest, then the darkest, what was left were the mediums. I've never made a bargello, but I think the concept is the same.
Love the fabrics and colors you have selected!