If they have been well fed their entire life, they generally won't fade, but not always.
If they have had a medium feeding schedule or pre-mature end to fertilizers, then yes, they generally will fade, but not always.
"The Fade" is not a necessary process or requirement for determining harvest maturity.
However, most people generally stop all fertilizers, feeding, supplements and stimulants about 2 weeks before the estimated harvest date and this may lead to a natural fading occurring.