Uneven aging and discoloration of wood flooring is often caused by rugs on the floor. The rugs block the UV light causing uneven fading. Sometimes rugs also bleed and oil onto or into the wood flooring. If the rug area is oily, then it can usually be wiped off with wood floor cleaner or dish soap and water. If the oily residue is then gone from the surface and the floor is still discolored, then the oil has seeped into the finish and the floor will need refinishing to correct the problem.Discoloration is also caused by the finish darkening with time. Some water-based products may not darken and others just darken slightly. Other water-based products that are emulsified with oil particles have a slight yellow tone in the bottle and these will darken and yellow over time. Oil polyurethane finish darkens and gets more orange with time and exposure to UV light. The color change is directly related to UV light intensity and exposure.The wood itself will also change color over time. A few woods like, Cherry, Pine, Tigerwood, Brazilian Teak (Cumaru), Brazilian Walnut (Ipe), and Brazilian Cherry (Jatoba) will darken with time and exposure to average UV light. Most other woods will lighten with time and UC exposure. For example, a standard red oak floor will initially be darker and more varied in color. As it's exposed to more UV light, the finish will darken slightly but the wood will bleach out and lighten. Everyday, direct sunlight will drastically lighten the floor to a point that it's pale without its original color variation.Once the finish or wood has discolored there are only two options: Wait months or years for the fading to equalize throughout the entire floor, or sand the floor and hope the wood discoloration is shallow so it can be removed. To prevent discoloration, check and move rugs more often with flooring that receives direct sunlight.