How would I go about making these arrows more intuitive and informative?

Currently, in an each of the rows of a table I have an arrow attached.
Which, depending on whether the some number on its right has increased or decreased from the last time, changes its direction; thus, users don't have to click on a row and check the popup menu to figure this out, and they can just see it right when scrolling over that table.

My arrow also changes its colour - from bright orange, to dark almost black colour, depending on when was the last change committed to that row's number.

I thought it's okay and pretty intuitive, and my client understood what arrow directions mean, but didn't understand what colours do.
I also think they didn't even notice the difference between them (the colours)
(Generally, all they've been looking at for their life in computers was Excel and iOS ui, so my web app's UI is unusual for them.)

Here is the picture of what it looks like right now (Arrows on the left):

I need help in figuring out how to make these arrows more intuitive, so that I won't have to put a "map legend" somewhere on the page (they should tell how far in the time were last changes committed, and they also should show a direction depending on whether change was positive or negative).

Thanks in advance.