Nice set of shots, Dale - and a good job experimenting. Yes, Liz's stars were darker than the background they were on, which made them seem black. All very interesting - to see how much they can change with all the variables.
Except my stars were NAVY BLUE. They were a darker BLUE than the vivid blue background field: not grey on a darker background field. http://www.pbase.com/britestar/image/164021249 So this is still "different". LOL.