For the hell of it, I took the test with my much-used iMag G5:
This screen has some magenta-yellowish tinge on the right side of it, but very subtle. It also has a white stripe along the bottom (some burn-in of some sort) and burn ins on the right and lower sides from much use. The shadow on the left side is just a result from camera.
I hadn't even noticed the magenta-yellowish tinge until after taking test.
My conclusion?
1. Tests with cameras are ********.
2. Macrumors members now have an over-stimulated awareness of lcd screen color un-uniformity-- too much for their own good.
3. Macrumors members would sooner attack screens for displaying yellow tinge than blue tinge. A lot of those screens look damn blue to me.
Your iMac G5 actually looks great... the problem with some of the pictures posted here illusrates is that there is a significant difference in the colorshifting (it looks to me). If your iMac has a similar problem then this could mean the yellowing isn't just limited to LEDs. Otherwise yeah I would not trust photos unless it shows a significant difference.
edit: It turns out the older iMacs have had this same issue before. Also I am not sure if they are IPS panels. I believe that LEDs are suppose to give consistent backlighting while IPS gives color consistency in very wide angles.