Disquo Bleu appears to have been a one-off label, issued in collaboration with Rough Trade. Its first - and only? - release was a single by The Monochrome Set, 'He's Frank' (BL-1), which came out in December 1979. The band's next single was on the Rough Trade label proper. Thanks to Robert Bowes for the scan and for bringing the label to my attention.
Copyright 2008 Robert Lyons.