What coloring is implantation bleeding usually?

I’m like 8 days late for my period, I do have irregular periods though but they always around this time for the most part. I went to the bathroom this morning and had a little brown color on my underwear. Like a very small amount. It wasn’t even enough to be considered spotting. I took a pregnancy test about 5 days ago and another 4 days ago and they both came back negative. Is there any way what I just experienced was implantation bleeding? Or a possible start to my period? When I wipe now, no color comes out.