I'm using GIMP to do the editing in the png file I've shown below. On selecting one of the arrows and trying to paint it red, the colour just does not turn red. It stays grey. I'm just unable to make any changes to it.
I'm a newbie to using GIMP, so do let me know if it has something to do with the layers or channels etc. How do I alter the icons in the png file?
ps: The image is from one of the jQWidgets themes (MIT license)