I save mine as pngs, but they're lower-resolution - listings only show 570 pixels-wide photos anyway, so you don't need a huge high-quality picture - you can have small high-quality pictures instead. ;) All my item photos (the ones that aren't saved at 500 pixel width so they look good on wordpress and tumblr as well) are in the 600 to 800 pixels width range. 72 dpi.
Your pics look really bright to me, too, with yellowish highlights. Maybe your monitor is darker or has bluer highlights.