There's been a teensy bit more details than that, e.g. [1]. If you think about exactly the file semantics that Bigtable would require (append, pread) that's exactly what is provided. Note that Colossus and D are two separate things. Google systems can use D without Colossus and a long time ago people used Colossus without D, although today Colossus/D is implied. The presentation gives the broad strokes of how Colossus is able to bootstrap itself from Chubby. It helps if you've also read the Bigtable paper [2].
1: http://www.pdsw.org/pdsw-discs17/slides/PDSW-DISCS-Google-Ke... 2: https://static.googleusercontent.com/media/research.google.c...