The 2MB limit is set on your server for processing PHP scripts in general, you need to ask your ISP to change that values if you do not have access to your php.ini. Please read here too: http://www.zenphoto.org/2007/12/troubleshooting-zenphoto/#11
Regarding the color tones: You mean they are less saturated? That is surely a problems with color profiles of the files. Your images probably contain such a profile but as far as I know except for Safari (at least on Mac) no browser is able to handle those profiles, so photos can look a little bland. I guess you used Photoshop to reduce you images, so you could try to change the "proof setup" to use your monitor RGB. You will probably see that thte images are more bland then, too. You should therefore always upload images without any color profile. Color management is a really difficult topic in general, I suggest you try a google search on it, too.
I hope that helps a little.