Yes ranking, not wa.... oh never mind

Quick question, more out of curiosity than for wanton spamming

When you start as a new member, you’re classed as an ‘XR Lurker’ with 0 posts, then you become an ‘XR Junior’ with a yellow box under your user name/avatar. Once you’ve amassed X amount of posts, you become an ‘XR Member’ with 2 green boxes under your user name/avatar, it goes on as seen below,...
XR Pro and 3 blue boxes
XR Master and 4 red boxes
XR Pro (again) and 5 red boxes
XR God (lol) and 5 purple boxes
So my question is, what do the coloured boxes mean, and what is the post count for each ‘section’ ?