So, here are my suggestions for the most prominent icon issues in the application. I've concentrated on the permanently present icons in the main tool bars but I'd very much like to continue my work on the remaining icons, probably starting with the ones in the text editor. (tracking, small caps, all caps etc)
The main idea is to group related icons by color to lessen the massive "wall-of-icons" impression that newcomers may experience. Now, I might have gone too far but at the same time some grouping is better than the current situation. As a bonus, the text icons really look neat on a dark menu background as well.
1. All icons for entering some kind of (content, text, image, table, render-frame) has a blue hue.
2. PDF-icons have some kind of red hue which can be associated with the use of red colors in the Acrobat PDF viewer.
3. Drawing icons (will) have warm tan/yellow hues, like the existing freehand, caligraphic, measure)
4. I'll probably copy/redraw most other icons from the current GIMP set, improving wherever necessary.
So this is 12 icons re-hashed or redrawn from Tango and 1 original (measure), I hope they can be of some use. I'll certainly continue my work on these and will probably complete the concept some time in jan/feb with an update right after christmas.
Finally, as you may see from the mock-up, I also suggest using de-saturated or paler versions of the icons as identifiers on all the different types of frames. At least with the PDF-elements, they all look exactly the same now and are quite confusing to use unless you have the Outline panel open at all times.
Edit: Source SVG added.