My doc told me if you're going to spot, brown is what you want. It basically means it's old blood (either from ovulation or implantation, etc.) that is just finally making it's way out, so don't worry too much. Pink/red is what you'd want to look into further.
Digis are notoriously unsensitive, but it also depends on the digi. Is it a clear blue weeks predictor? In my case I got a positive on that 3 days after I got positives on an FRER. As long as FRERs are getting darker every couple of days, I wouldn't worry about the digi!