"the value for blue was closer to 0.11"

The weight you gave here is very close to what tachyon had, and I will try this. Thanks for that link, I think you are right, I will look into it, and find a way to use YUV.

The diffculty for me was not really the calculation of the difference, as that part seems to work okay. The problem is really that, for certain color combinations (background and foreground), the result is poor, that's why I am getting into the big question "what is color?". Your post and links are very useful and helpful. Thanks.