Hello fellow Griffith users !
First of all, have a look at how I see Griffith on my computer:

That's right, different icons for the five extensions, the stars and the seen/unseen symbols!
Interested? You will find everything in
this zipped archive file. Put it in the directory <path-to-griffith>/images, unzip it there
after having saved (renamed) the original files 00.png -> 010.png, as well as seen.png and unseen.png, otherwise they will be overwritten!
Read the instructions in README.TXT (or LISEZMOI.TXT for the French speaking users) to change the extension icons (it's just one line of code in each extension that needs to be modified).
The SVG and XCF versions of the icons are also provided in the zip file, so you can change them yourself to your liking. If you are not interested in doing so, you can delete the directory <path-to-griffith>/images/SVG-XCF/ that has been created on your hard disk.
The original SVG icons have been taken from the Gnome set and have been modified with Inkscape , I suppose it is allright to reuse them as far as the licence is concerned, I must confess I didn't find any information about this.