Undertone picks the side. Contrast sets the volume.
Contrast is how far your hair, eyes and skin sit from one another. It can be low, moderate or high. Depth doesn’t tell you your contrast, so don’t guess it from depth. You read it on your own face, and how to read your contrast walks you through it.
A strong gap supports a strong mouth: deep red, plum, burgundy, a vivid pink. A softer gap asks for a softer texture, such as satin or a sheer wash of the same color.
A low gap doesn’t ban a bold lip. It asks you to change the finish, not to give up the color.
In my view, a bold mouth on the right side beats a timid nude on the wrong one. And some days the loudest shade is the right call, for a big presentation or a night out. You can step up one notch without crossing to the other side.
Finish matters too. Matte gives a defined edge, satin softens it, and gloss adds light. A liner half a step richer than your lipstick, on the same side, frames the mouth. Test the lipstick with the foundation you wear and with a bare face, because your lips sit differently against each.