Hi,
first of all thank you for this great application. The only qualm I always had with it was the colourful icon set that didn't integrate too well with the stock monochrome indicator icons under Unity. So I created a custom icon set to go with the monochrome theme. You can download the icons here:
http://imgur.com/a/nhW1T
In order to install them you will have to replace the corresponding icon files in the icon folder and then compile goldendict from source.
Greetings,
Glutanimate
Edit: updated download link