This also happened to my Jeep. It actually looks like a glare from the sun, upon first notice. As such, I just ignore it (the fading).
1998 TJ Moss Green Sahara w/ numerous scratches & dents whose playground is on a tropical island that's 33 miles long and 4-12 miles wide, in year-round 82 degree weather
Edit: "Now jeepin in Oregon"