Nose pads are made out of clear plastic. They are in constant contact with your skin, and underneath the plastic, the skin often sweats. The sweat, over time, causes the nose pads to turn yellow. On average it takes about one year for the nose pads on your glasses to turn yellow, and you probably want your glasses to last longer than a year, particularly if you are paying a lot for designer eyeglass frames.
Therefore fix your nose pads don’t replace it!!