The other night I was at a family gathering and two of my second cousins ( I don't even know how we're related ), landed up in this beautiful red flowing gown. Both wore the same. One had a light make up to go with it and looked stunning, trust me. If you happened to glance at her sister, you'd never imagine they're related. How can two people wearing same dresses give such a different impression?!
On better observation I realized it was the 2nd girl's bizarre lip colour that made you wanna look away. Also this isn't just one incident, I have often observed girl's with no sense of applying the right colour to their lips.
So here are some handy tips if you're confused girls.
NO DARK REDS AND BROWNS PLEASE! Let the middle aged women enjoy those colours.
If you're going out in the day for a casual outing, stick to light pink or toned down scarlets. If the outfits are dark, opt for simple plain glosses with tints of the colour of your shoes or t-shirt.
For a formal day wear, go for a bolder colour. Say red with black. Make sure the red is not maroon or fancy in anyway. And to give it a soothing effect, press your lips to a tissue before you leave.

Nights can be glittery and fun. Make a statement with silver and mauve. Purple and mud brown. Depending on your outfit.
Trust me when a guy looks at you, even if he says you've got pretty eyes, he definitely stares at your lips.
Good luck.