I hear you, Craftymel... I have gotten myself off on a direction and then gotten stuck and refused to go backwards, just driven myself nuts getting it figured out! I love the image of your blue floor, it reminds me of my own studio floor during some of the color challenges!
If you feel like it would help, why not post thumbnails of the color combos you are considering and people can take a look and make suggestions? It sounds like you have a great card idea and have invested a lot of work in it already. The perfect BG color exists, you just need to pin it down!