Something to play with, or maybe just discuss...
Sometimes the icons could use a bit more contrast, especially when they are a light color. This patch adds an (optional) shadow that can be displayed under the icons to give them a bit of extra contrast and definition.
The color of the shadow is determined automatically based on the brightness of the icon color. So black for light icons, and white for darker ones. The user can select the shadow opacity and the offset. The opacities for light and dark shadows are set separately in case you like one but not the other.
The following illustrates a fairly common result, with light icons on a dark field. The top section shows what it looks like currently, and the bottom section what it can look like after this patch:
Here is a more extreme example with a theme that has mostly dark icons and some light. You should see dark drop shadows on the shading icons, while most dark icons look a bit embossed. But again. you can turn on the dark shadows but turn off the light ones if that is your preference.