Anchor to what already works
Ask which lipsticks the client reaches for and gets compliments in. Those shades encode their undertone preference better than any swatch fan. The blush should feel like a natural, everyday version of that palette.
Adjust for biology and time
Filter the desired shade through their natural lip colour (hold a clear glass slide or just observe the bare lip), lean the pigment choice a step warmer and a touch brighter than the goal to survive the cool-ward fade, and add a corrector base if there is any blue, brown or grey to cancel.
De-risk with a test
For deep lips, strong colour changes, cool targets, or higher Fitzpatrick types, place a small test area (e.g. inside the lower lip line), heal it four weeks, and photograph. It is the single best predictor of the real result and turns a guess into a decision.
Document
Record brand, colour name/number, any mixing ratio, batch and expiry in the client file, so a colour that heals beautifully can be reproduced at the boost — and one that does not can be adjusted.
