Blue blobs represent the 1960s (plain for William Hartnell, dotted for Patrick Troughton)
Green ones represent the 1970s (plain for Jon Pertwee, dotted for Tom Baker)
Yellow ones represent the 1980s (plain for Peter Davison, dotted for Colin Baker, pins for Sylvester McCoy)
Red ones represent the contemporary series (plain for Christopher Eccleston, dotted for David Tennant and pins for Matt Smith)
In addition orange envelopes are other bits of Who-related information taken from the so-called real world.