Lovely portrait quilt.
As for the tulle - I took a class with Bonnie McCaffrey where we used tulle to cover the quilt before quilting. She did a demonstration about how different color tulle can make a huge difference in getting the look you want for your quilt.
A black tulle or another color may make your quilt pop even more. The silvery grey may not do that. If you can take your quilt to a place that has a lot of tulle colors you can try different ones.
I was thinking that a dark purple may be interesting!