To set some context: any porous natural material used daily in a wet bathroom environment will change in appearance over time - this is expected and unavoidable. White grout in a shower is a good comparison; it is installed white, but exposure to water, soap, and daily use means it will discolour over time regardless of care. Nobody would consider this a product fault.
The same principle applies here. We have sold thousands of these mats and rarely receive complaint of this nature. The most likely explanation is exposure to soaps, shower gels, body oils, or cleaning products, which can saturate the pores of a diatomite stone mat over time, impairing absorption and causing surface discolouration. This is not a product fault; it is a characteristic of the material when exposed to substances beyond water.
