What Make Stithes Turn Black After Labiaplasty ?

Hi. I recently had a labiaplasty and the stitches I was given were originally white. I am now 2 and a half weeks since surgery, and a few stitches at the too have turned black. I wanted to know if this was normal? Does it mean they are dissolving or ready to dissolve? Or have chemicals in my wee perhaps changed the colour?I m so worried, let me know, thanks!