Normal exposure to sunlight, heat, air conditioners, etc. will bring about natural changes in the original color as the floor ages. If possible, use blinds or drapes to protect floor from excessive sunlight. When some areas of the floor are covered, as in large furniture pieces and area rugs, the change under these pieces can be lighter than the surrounding floor, as they are not exposed to the same conditions.
This is normal and is not a defect. Rotating the position of area rugs and furniture from time to time will allow the covered areas to slowly adjust in color to the surrounding floor.