I am Assuming the fenders are Plastic , right ??
If they are, one option is to use a good quality spray paint... Do Not use "Gloss Black" or "Flat Black" though.. There is one that is inbetween gloss and flat.. "Satin", I think its called..
And Be CERTAIN to Use the Expensive cans of spray paint.. There is a reason some cans cost $6 ea and up...
Of course, you will have to use some kind of cleaner to prepare the plastic for the paint.. Something you can rub them down with to remove any waxes, tars or other substances that paint disagrees with..
If you do a good job they will look like new....