I have a mat at the front do or and when I moved it the colour of the floor under the mat is lighter than the rest of the floor. Why and how can it be fixed - POLYCURE

Sunlight will cause colour change in all timbers. Removing the mat for a while may allow the area under the mat to “catch up” with the colour change in the rest of the timber  and even out the colour of the area. If this does not fix the problem the floor may need to be sanded and recoated.