Icons are one of those "black arts" - it's very hard to create images that "work" at such tiny resolutions, and resized photos look like blobs when they're that small. If you can't draw to save your life (like me), you're in real trouble.
I'd guess that Admin has made use of what looks like icons from the rather nice Silk' set that's freely available for a lot of the UI-related stuff, but unfortunately these are 16x16 and don't have icons for stuff like furs or marble in there, so it's a matter of cobbling these kinds of images together from anywhere that's practicable (and preferably copyleft/royalty-free). Having them all the same size is simply to make them appear more consistent when displayed on screen, I'd imagine.
Personally, I don't think that the icons for the resources are bad at all - it's definitely fixed on of my pet peeves, which was that marble and sugar looked a lot alike (in the sense that they were both vaguely white cubes). (I still have this issue with Asphalt and Construction - maybe you could use a picture of a road surface for the Asphalt one? This one's 29x21, I think, but you might be able to scale it okay if you are/have someone slightly arty to have a bash at redrawing it?)
Having said all that, I think that these images are meant to be symbolic, so I don't think that what the icons look like is that important as long as people can tell them apart.
Why do you have issues with intercolour treaties? And if people think so badly of the purple sphere, surely that'd rule out intercolour treaties in the first place? Er, did you mean intra-colour?