Depending on your water quality, it is common for the Ceramic Filter to turn from bright white to beige or yellow.
It means that impurities, dirt and sediment are stopped for filtration, leaving the surface of the Ceramic Filter discoloured.
Simply scrub the filter on all sides with a soft brush and cool water. Scrubbing the filter will unclog the pores and expose a new layer for use. NEVER use detergents or other cleaners!