Why warm is the default
Two forces push healed lip colour cooler over time: titanium white frosting, and the faster clearance of warm fractions. If you start cool, you finish very cool — grey, mauve, ashy. If you start warm, the drift lands you somewhere natural.
Warm colours also sit more harmoniously over the red of real lip tissue and suit the widest range of skin undertones.
When cool works
Cool, blue-based pinks and berries can heal beautifully on clients with cool skin undertones, fairly neutral natural lip colour, and no hyperpigmentation — and even then most artists underpin them with a thin warm corrector layer so the fade has somewhere friendly to go.
Reading the room
Ask what lipsticks the client actually wears and looks good in. Someone who lives in warm terracottas will hate a mauve blush; someone drawn to cool raspberry may be disappointed by brick. Match the pigment family to their existing palette, adjusted for fade.
