My eyes are extremely sensitive, and I have a hard time finding eyeliner that doesn't irritate. I discovered this one several years ago, and quickly became my favorite. I tightline from underneath the lash line to frame my eyes and give the appearance of thicker lash roots, without looking like obvious makeup. I love the short, stiff brush (felt tip?) that allows for complete control without flopping around. I dot pigment between the roots of individual lashes, and then I connect the dots. It never smears all over the water line. Bonus points for a brush I don't have to wash.
I have very fair, pink-porcelain skin with dark ash blonde hair (10% grey), and Black is not too harsh when applied under the lash roots. It adds a subtle frame, more than an obvious line. Still, I would be over the moon if Revlon offered this liner in a blue-tinted sooty grey. (The Brown was too warm for me.) The bottle goes into my daily makeup bag, and it has never leaked or dried out.
This product stays on all day--though it would fade if I had a good cry. Unlike other brands' gel formulas, the Revlon ColorStay Liquid Liner easily washes away at night with my usual cleanser.