This example works for all shades pink, red, purple, blue. But you won't stop there- it's then your job to blend the edges so you're not reliving a terrible 90's trend. For example, if you have a milky nude shade like Myth but don't want it to look sooo pale, you can take a lip liner with a darker base (stripdown, spice or oak) to line to define. The fun thing about lipliners is that they don't have to perfectly match the shade of lipstick you'll be wearing. They now have an insane color assortment perfect for any lipstick you may own. MAC lipliners are among my favorite lipliners on the market. Lipliners can also perfect and balance the lips to create symmetry, shape and volume.
This comes from first hand experience working with reds, purples and pretty much any color that isn't nude.
Lipliners are one of my favorite makeup products because without them a red or deep lip color just may look crazy. As we get more into makeup and continue experimenting with the perfect lip shade to compliment our skin tone, we'll soon cozy on up to using lipliners.