What are the color bars on the left side of the history screens?

What do the colors in the tag history screen represent? Do they represent the number of days passed since the change, or the general reaction by users towards the change?

The color bars also appear on the note history screen, but are not on the other screens like wiki edit or comment history.

I asked the same question a few months ago.

http://danbooru.donmai.us/forum/show/39239

Oh hell beaten and sort of wrong anyways.

葉月 said:
The bigger the difference in hue, the bigger the difference in post ID. They're meant to let you see when somebody is working on a whole series of posts at a glance.

From what I see the colors start from black, then brown, red, yellow then green. So, two tag edits to the same post will result in a black, and two tag edits to posts with very different numbers will result in a green, right?

It's kind of hard to tell with danbooru but if you use 3dbooru's general tag history it's easier to tell. Particular colors don't really mean anything specifically.