Does the darker the line mean less thc metabolite content?
Contrary to popular belief, there is no meaning attributed to intensity or width of the lines. Assay kits have no ability to quantify metabolite levels (unlike the GC/MS) - they are simply a quick go/no-go analysis. To say that a darker line means less THC metabolites would be speculating.

If a line appears in the 'T' window, even a faint one, its still a negative.