YSL Rock'N Red (8) is a cool red with a luminous finish that is limited edition and retails for $38.00. In comparison, Guerlain Rouge Saphir (821) is a cool red with a natural finish that is discontinued and retails for $58.00.
Guerlain Rouge Saphir (821) is 90% similar — it is less shimmery, darker, cooler.
