Are all app backgrounds PNG images?

[ColonelKernel]

Hi, are all app backgrounds PNG images or can we just specify RGB hex values in the CSS?

I've got the Rough Cuts book, bookmarked all the sites, am digging through the SDK and everything else I can find, but if someone could answer this for me it'd save me some time searching for what I'm thinking of.

Further, I know stylistically that Palm wants nice and cool smooth fades, but my first real test project requires single tone backgrounds.

Thanx in advance.