Rather than taking a picture of the quilt, at which point it is too late, put your fabrics on the copier bed, one at a time and make a black and white copy. Then you can see the value of each fabric in relation to each other. Arrange those copies in the way you think it should be. Then using the actual fabric swatches, arrange them the way the copies indicated, and black and white photo copy that. If there is any glaring mistake in value, it should show up then. This should be the way your Bargello will go together. I've done quite a few bargellos, and if I have a question in value, I do this. But as you do them your 'eye' gets better and you it's easier to tell value. Also, remember that only a tiny part of the fabric is going to show, so try to stick to fabrics that read solid.