This has been an issue that's bothered me since ARR. For some reason lip colors only show any real changes if you're a darker skinned character. For paler skins you have a faded off colored of the line you're on, and the darker you try to make it, it starts to look more like a faded black than the actual color you selected. The only skin colors that don't seem to suffer this is are darker browns, grays, blues, greens, and purples.