Getting a period right before a BFP?

Ma
Has anyone had an entire period with dark brown, almost black blood and then found out they were pregnant? I had a three day period like this(which came on the exact day I was expecting my period), I'm ttc and wondering if there is still a chance of pregnancy since the blood wasn't bright red like it usually is? Or am I just having a very irregular period? Any insight or advice on this matter would be appreciated!