What is "copper blue"

Copper Blue is the debut studio album by American alternative rock band Sugar. It was voted 1992 Album of the Year by the NME. All of the songs were written by guitarist/vocalist Bob Mould, who also co-produced with Lou Giordano. The song "The Slim" is about losing someone to AIDS. Musically, the band continues the thick punk guitar of Mould's previous band, Hüsker Dü, while slowing the tempo and emphasizing melody even more.