How dark are your OPK's before AF?

I am 9dpo, and yesterday at 8dpo I had a hint of red spotting in ewcm with cramping (definitely NOT ovuating again). After four children, I fee it's most likely implantation. Today I had a darker OPK shown below (clearly not yet positive). I test daily just to watch the fade, and this caught me off guard. Could this be due to a possible implantation/HCG beginning? How dark are yours around this time? 
Also, I'm waiting until AF is due to test!