I actually did another OPK this morning and i got a stronger line than yesterdays one. Yesterdays was only slightly fainter than the indicator line but this mornings one is as dark as it. Not sure what to do now, i dont know if its possible to 'O' twice in one cycle or not, if so then thats prob the case as my cm has increased.
In saying all this though af was due yesterday and still isnt here.
Good luck.

So yes it does get darker to answer your question.