As far as I know all 2013 F6B and GL1800 use the same front fenders. You could buy in 2013 a GL1800 in a Light Silver Metallic, Gray Metallic, Ultra Blue Metallic, Candy Red and the F6B in Black and last but not lest Red.
Then since all F6B and GL1800 2013 till 2017 run the same front fender there are many more colors to chose from like White, Yellow, matte colors, shinny colors and so on. I'd find the matching color fender.... to heck with the year and put it on. Now if it is an off color from a custom paint job then a repaint may be in order.