The 'yellow tint' actually just reflects Apple's choice to use a warmer look to the screen. According to comments by Apple, it was intended to make the display feel more natural. A software change to this setting is not out of the realm of possibility but according to Bob Borchers, Apple's senior director of iPhone marketing, there are no plans to change this at this time.
Ars Technica, however, claims the 5A347 firmware does indeed "fix" this problem:
We have confirmed that updating the firmware from 345 to 347 changes the color calibration to be less yellow. We did this by taking an iPhone purchased at an AT&T store on Friday (5A345), restored and updated its firmware, and compared it to other iPhone 3G models running the 5A345 firmware and 5A347.The 5A347 firmware in question is the same firmware that was leaked a day early and installed on many of our original iPhones. The firmware comes from Apple and is intended for iPhone 3G use only.
This firmware is still available, but only when you click on "Restore" in iTunes. The actual iPhone 3G ships with 5A345 firmware which is not upgraded automatically to 5A347. However, upon restore, iTunes pulls this newer firmware and uses it.
Ars warns that the upgrade will take at least 30 minutes.