Red fades the fastest, but I have seen first hand how the dark colours in colorbond roofs (and some tiles too) fade faster than a light colour. Go to a new estate, and look at the colour of the roofs, and then go to one that is about 2-3 years old and look again, you can see the same shades and they look faded. It's something we've noticed looking at display homes for the past year. And we know it isn't a different shade because it fades in patches. (Like we were in a South facing street in an estate that about about 4 years old, one part of the roof facing West was a bit lighter than the South side). I doubt people would notice it that often, but we have seen the samples and have realised on cloudy days the roof isn't glarey and you can see it. And that's only a few years too.