Yeesh, what a change. If I didn't look closely I'd think someone swapped your rooster out for another!
I've had the opposite of this, where pure whites turn black/red/yellow etc in a year, in that case it's due to them finally receiving full enough nutrition to display their true type.
In this case, well, even severely malnourished chickens don't tend to go white in one year or even necessarily within their lifetime, they just tend to lose color over generations and display rapid-fading feathers, provided it's not acute enough deficiency to kill within a year...
I think your rooster may have possibly a thyroid problem. Lack of iodine can cause color weakening or loss. That said it's not the most common result of insufficient nutrition or thyroid activity. Some genetics bleach out very easily, but I've still never heard of a chook going pale as severely as this in one year.
Reminds me of something but can't quite recall at the moment... Will look into it and see what others reckon, should be an interesting thread.