Well, you may not of even realized that this is a problem but some folk have reported that when taking a photo under fluorescent lights with their iPhone that a blue stain appears in the center of the camera.
Well, guess what? There's an app to help you out - blue tint cleaner - take a look...
I haven't tested this app but am looking forward to doing so. It’s actually a standalone version of the feature from the developer's camera replacement app, FinderCam.
I also suspect that this app will work with other iPhone's not just the iPhone 4.
I'll let you know how I get on with the testing, but it certainly appears like a useful addition to your photo apps toolbox.