That color scheme was allegedly picked for visibility on very low-end TV sets. (The Amiga palette colors could be chosen arbitrarily from 4-bits per channel RGB, so that wasn't a constraint.)
(The icons weren't just arbitrary sized, they could have different pictures for the selected and unselected state. You see this with the open vs. closed drawer icons (drawers are like "folders" in other OS's) but many app icons also used this effect.)
Be that as it may, if you look at C64 GEOS which ran on consumer TV sets and with comparatively primitive hardware, the UI looks so much nicer in GEOS to my eye. Even the Apple II GEOS makes Workbench look like a hot mess.
(The icons weren't just arbitrary sized, they could have different pictures for the selected and unselected state. You see this with the open vs. closed drawer icons (drawers are like "folders" in other OS's) but many app icons also used this effect.)