I am happy with this rear fender. It bolted on easily, and it looks nice. The only slight negative is that the gap between this fender and the plastic on the bike is wider than the gap with a stock fender. Not a big deal but a smaller gap would have been better.
Unfortunately, Acerbis does not make a fender that replaces the rear fender on your Yamaha TTR225. The only option I show that we would carry would be the OEM replacement rear fender: http://www.motosport.com/dirtbike/oem-parts/YAMAHA/2001/TTR225/FENDER?sku=4VW-F1611-20-00
Unfortunately this fender is not available in black for your 1998 KX125. We can get one for you if you are able to give us call. The part number for the UFO rear fender in black for your bike is ZPU12-174-33.
The images and colors may vary per application, this version is a replacement to fit your bike WITHOUT the taillight but if you go back on line and list your ride again then select the UFO version it will look more like the image and have the Taillight.
It will not come with a light, im not 100% sure if it will line up right. if not try re-drilling the holes to the right place maybe, if thats not in your mind then just send it back to motosport their customer support rocks.