Because it is an overlay, it does not alter the underlying skin color but instead adapts to it, making it "slider friendly" and compatible with other CAS modifications. Difference Between "Skin" and "Skin Overlay"
Available in four different strengths or opacities, allowing players to choose how subtly or intensely the details appear on their Sim. Harry Skin Overlay by MSQSIMS at TSR
It is found under the Skin Detail category in Create-A-Sim (CAS). Because it is an overlay, it does not
MSQSIMS often releases two versions of their creations: a "Skin" and a "Skin Overlay." Understanding the difference is crucial for players: Harry Skin Overlay - The Sims Resource Because it is an overlay