From what I can surmise of the other thread:
The colors are based on the hex values of its RGB components, as discovered by djohnsto77 on page 14.
Originally posted by djohnsto77
Ok, here's what I have:
The red component of the color (the first byte in the hex color code) is determined by applauses. The value is the number of applauses you have + 50,
with an apparent minimum value of 52 (values in decimal).
The blue component (the last byte in the hex color code) is easy, 0 for non-staff 128 for staff (decimal).
Now the green component (middle byte) has been giving me trouble. It's definitely related to number of posts (like the length) and seems to range
from 50 - 250, increasing with number of posts up to 10,000 (again like the length). The exact way the figure is calculated though escapes me, it
looks like it's either a sliding scale or just predefined ranges without an equation behind it, I'm not sure.
As far as people who don't have bars, I think it's just that the system hasn't calculated them yet for some reasons, although there's a
possibility that too many applauses or posts could "break" it, but I'm not sure about that.
OK....there you go.

As for having a second bar, it seems that after 10k posts, you get a second bar. The meaning of the colors on the second bar is still not certain
except to SO.