Since I upgraded from 14.04 to 16.04 I've been experiencing problems with viewing the standard icons that come with Ubuntu. The icons appear as being too light and are therefore not clearly visible. When the icons have text next to them this is not too much of a problem but when they do not, I am left to guessing the button's functionality.
In the attached screenshot of my desktop you can see Inkscape running in the background with the XFCE panel menu opened above it.
The horizontal red boxes highlight the unclear visibility of the icons within the menu, and the vertical red box demonstrates icons in Inkscape that also appear as being too light which also do not have text (so their functionality is less obvious).
I've also tried changing the theme and default icon set but this has had no effect, the monochrome icons persist.
How can I change these icons to another icon set that is more clearly visible?