OPK help

I'm on day 2 of using my first ever opk. I know you will always pull 2 lines but it isn't positive until your test line is as dark as, if not darker than, your control line. My question is this: will the test line always be the same color on a negative? I tested at the same time yesterday and today and can't tell much difference between the 2. Both are negative. MAYBE the one from today is a hair lighter but they're close. After you surge, will the test lines gradually fade to a feint line or will they all remain sort of dark?