What does a darker grey arrow in finder represent?

I use Finder with the 'view as list' setting. Today I noticed that one of my folders had a darker grey arrow next to it than all the others:

(The notes folder is the one with the darker arrow)

I then took a copy of the folder to see if the copy would also have the dark arrow, but it jumped to a different folder! (now tests_and_trials)

I closed and reopened the finder window, and all the arrows were light grey with no dark grey arrows at all.

What was going on?

(This is on OS X 10.9)

Solution 1:

This is simply a glitch. The darkened triangle is used when the button is pressed. It doesn't mean anything about the folder and will be fixed by closing and re-opening the window as you discovered.