Here it is... I found it! Bonnie Hunter's tute on selecting neutrals for the backgrounds. You may be surprised:
http://quiltville.blogspot.com/2013/...-neutrals.html
Another trick for deciding which fabs could be background 'neutrals' was to hold the fab in question in front of my pile of darks (for stars) and also hold them in front of my pile of neutrals I had already selected. Then you ask yourself which they blend with better, and which they contrast with... sometimes you have to squint to see only the value.