Hello,sorry feel silly asking as its not an important question,but it bugs me.I have tried lots of different opaque tights from 60-100 denier,and i keep seeing i thought at first was a flaw but i have this problem with lots of pairs,today i have just opened a pair bought from John Lewis and both legs have like a black line running through them,the tights are always black but when i look down i see this mark and it annoys me,i wonder why this is happening.I have seen it with other women and with women wearing leggings just looks ugly would there be any reason for this?Thank you.