MAC Russian Blue is a cool gray with a matte finish that is limited edition and retails for $17.00. In comparison, NARS L'Amour, Toujours L'Amour #4 is a cool gray with a matte finish that is discontinued and retails for $25.00.
NARS L'Amour, Toujours L'Amour #4 is 85% similar — it is darker, cooler.