A number of people I am working with were curious as to what color depth the system software runs in. I suspected 32 bpp [a b g r], one byte for each component, but others were wondering if it wasn't running in 16 bpp with downsampled images/software alpha blending.
Funny the way I found a definitive answer. I was browsing this site about color depth (http://www.freemars.org/jeff/webcolor/) on my PSP and the PSP browser reported it ("Your color depth is currently set to 32 bits." is shown in the web page, 3rd paragraph down). Like I said, I already suspected this because of the lack of banding in true color images/all of the nice alpha blending effects/the fact that it's a 32-bit machine, but this is good to know for sure for people pursuing frame buffer exploits.