BFP dark enough at 14 DPO?
Wow, this is making me feel better about my tests, taken approx 13-15 DPO (give or take 2 days--O was difficult to pinpoint this month). Like you, I found that the tests were not getting darker.
The purple tests are supposed to detect hCG at 10 mIU/mL and the blue should be the standard 20-25. It looks like the same brand as bremen used, and my result looks similar.