Color on the add doc button indicates age of the newest file. Gives users an idea of how recently something was added.
It is possible to change the display (value and color) with a custom function.
In this case 18 is the number of days of the newest file (falls into the lightGoldenrowYellow color below).
if (docsDaysOld <= 1)
else if (docsDaysOld <= 7) (2-7 days)
else if (docsDaysOld <= 31) (8-31 day)
Else (older than 31 – no color)