I would definitely see a doctor or email the surgeon just for peace of mind, but it's probably fine, since all sorts of weird stuff happens in the early days. (I had dissolving stitches, which is the norm these days, and I only rarely *saw* a stitch... and they weren't white. [They were also all supposed to be gone by 1-2 weeks in.] However, a stitch that popped and left a bit of tender skin underneath might well look and feel like that.)