Final answer:
The testing of foundation color should ideally be done on the client’s jawline. This is because the jawline provides the most accurate representation of the overall facial skin tone.
Step-by-step explanation:
When testing the color of a foundation, it should ideally be done on the client’s Jawline. The Jawline is the best spot for testing because it's where you can see the actual color of their skin tone. Your foundation should match your skin tone and blend with your neck color. Using the Jawline for testing provides the most accurate representation of the overall facial skin tone as it can show a median color between the face and the neck.
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