Totally varies. Some people have lines that get gradually darker before a positive before ovulation. Some people just have a positive and no lines beforehand. Some people have lines that get gradually less dark after the positive. Or a combo. So it's impossible to say
With OPKs the problem is that it isn't an exact science. It'll take a month or two to see what your personal ovulation looks like on them. Some people show a line like that the entire cycle until ovulation and others will only have a line in the lead up to ovulation.
With mine I always have a faint line and then it will go close to the same darkness as the control line for my positive. I usually only get that one dark line all month and it is only when I test in the afternoon, usually around 1pm.