If you use 3.1 and newicons there is a setting in in newicons prefs to use fast ram.
AFAIR (I'm still setting up my A4000 with a compact flash card) in 3.9 there is a setting in workbench prefs (?) that lets you use fast ram for icons at least.
Cybergraphx prefs has an option to use fast ram instead as well-but even then some chip ram is is still used, but a lot less.
If all you have is AGA then i'd just use magic workbench in 8 colours with one of its patterns or do a color reduction of a backdrop you like (or one of the gazillion available on Aminet) using the magic workbench pallette in PPaint, or ImageFX with high dithering settings (Floyd Steinberg worked best for me). Its still fast, looks OK and doesn't chew up a lot of chip ram.
