No I haven't experienced breakthrough bleeding before. I did miss my pill on Friday, but I took it Saturday morning and have not missed any since. But today I still have darker discharge then normal.
It may be too soon to tell. If you have been taking your pills on time everyday, without missing a dose and doubling up constantly, then the pill is effective. Have you experienced breakthrough bleeding before? I notice that the pills low in estrogen can cause that, especially if you miss one.
If it persists and the bleeding becomes heavier and longer, I suggest speaking to the gyno to rule out pregnancy.