There are post-based ranks and special ranks. A special rank's stars will always override those of a post-based one. Yellow stars are used for regular groups (which include post-based groups and early-access groups like N Forum Veteran, a group for people established on other well-respected naturist sites or otherwise known to be OK despite a low post count).
Blue stars are used for some special groups like female chat and global moderator. Green is used exclusively for staff positions, five stars are used to highlight a modertor in his area of expertise while four stars are used by a more generic staff rank I am currently modelling. Red stars are special and only used for forum administrators who display that title, which is currently only Lisa and Pisco, the latter being the owner of the site. We have several other users with admin privileges, but the title is not used frequently since unlike in other communities, it does not come with significant extra privileges or a superior hierarchial position.
Regarding the post count boundaries,
it is not that hard to figure it out yourself.
Most permissions are automatically granted or taken away by the system, most noticably some features opening up as your post count increases, but we can influence a lot of that stuff manually as well. Oh, and I have heard stories of big blobs of low-valued posts somehow simply not counting, so just posting for permissions is probably a bad idea.