Dude. Orange, black, blue and white. The GUI looked like it was in CGA at the time. One could comment that the Apple GUI of that era - being as it was in B/W (heck it may have even been 1 bit, unsure) - was equally ugly but you can at least say that the "choice" of colors on the Mac had a certain minimalistic functional elegance. The default GUI colors on the A500 were eye-searingly bad. Showing it in the ads would've made people laugh, not contemplate purchase.
Of course you could make the argument that it could be tweaked (and it could; I used mine in a pre 2.04 "greyscale"), but if C= had done that how many people who may have bought based on advertising would've gotten the machine home and, upon seeing the horror of 1.3's color choice, assumed it was "broken"?
Yes, well then they should have shipped it in a non-disgusting colour scheme then, with a menu pop up on first boot asking if they would prefare the hideousovision colour scheme for use on a TV or something.
My point is that nothing in those ads tell me it even HAS a gui. the mac ads of the time were all about how the mouse was awesome, that it was
so easy to do simple things, that there was cut and paste, that you didn't have to learn weird commands. The amiga advert gives me the impression that it's basically a multitasking C64. They've completely glossed over the most important part of the machine. Did commodore even know how important showing the MAJOR difference to the 8bits/PC was?