The phrase "purple liner" refers to a purple-colored eyeliner that is used to draw a line on the lower or upper eyelid for makeup purposes. Full definition
I used to wear purple liner a lot because I think it compliments brown eyes. (maybelline.com)
I love purple liner but it never fails, every single one I try is hard, dry and is like trying to line your delicate eye skin with a kid's crayon. (nyxcosmetics.com)
Main focus were the eyes, featuring a gorgeous brown - golden smokey eye, very subtle, with a vibrant purple liner on the lower lash line. (lindalibraloca.com)