Odd lined discolouration

Hi mums. Iam 6mths pregnant I am having discolouration. I can see generally I am becmin dark. But I notice down my leg both side at the back this weird line marked & it's darker frm there. Its not itchy, painfully & I don't see it like any varicose veins. But it's this line drawn down darkness. Any idea wad's this ladies ? Anyone hav ?