Dina, I am very impressed by your openness to the critique of others! And you've been well-advised in all of the above posts.
I've made a number of bargello quilts, and my advice is to not shy away from the lightest lights (even white, if necessary) and the darkest darks (even black, if necessary) in order to get optimal contrast. If I can figure out how to move a photo from my cell phone to my computer and post it here, I'll do so. It'll give you an idea of what I mean.