There are other icon sets on aminet. There are also palette preference settings for 4, 8 and 16 color workbenches.
You can look thru the galleries on this site and others and see what other people have done with icons, palettes, backdrops, etc on ECS machines. There is a member here (I don't see him much anymore) named Mr. A500 who left some excellent examples in the gallery. I think he managed some incredible graphics in just 16 colors. Some of his work:
http://www.amiga.org/gallery/index.php?u=2187If you colorize or make your own icons, it might be a good idea to first select a popular palette for icons that you like for compatibility.