Sometimes black eyeliner is a little too harsh. Say you've had a long night, maybe you stayed out a bit too late, maybe you decided to watch reruns of your favorite sitcom until 2 am because you just couldn't turn the TV off; these are occasions when black liner draws more attention to your bleary-eyed self.
Navy blue is a fun, and more subtle alternative. I've always been a fan of lining my waterline. If I'm running on empty and it's showing in my eyes, a pop of blue fits the bill for a polished but not over the top look.
Elizabeth Arden's Midnight Blue is a dark navy that is just perfection. It enhances the natural green tones in my eyes (hooray), doesn't look too made up for work and can easily transition into evening (just add a little more). It glides on smoothly, and the opposite end does have a rubbery tip that can be used to blend. Though, I prefer using my fingers. Needless to say this multi-purpose pencil is a permanent fixture in my purse.