C-LOCK Technology for long-wearing results that fight brassy hair. C-LOCK Technology gives the Cool Fashion shades a cool undertone with long wear results that stay true to tone for up to 8 weeks on chemically treated hair. There is reduced interference from other background tones, leaving your hair color cool and ashy despite your hair color history. The new Cool Fashion shades are great for people who want to be daring with their permanent hair color but are concerned about brassiness. They're perfect for those looking to mute warm undertones, with results that stay true to tone.