All wood changes color as it ages and gains its unique patina. This is the beauty of a natural product. In direct sunlight color change occurs rapidly and can be seen within days. The same color change still occurs in areas not exposed to sunlight throughout the process of oxidation, though at a much slower rate.
The "color aging" over time explains why the flooring "out of the box" may not match the color of the samples you chose your floor from.
Cherry: pronounced darkening from pale pink to deep red.
Maple: slight ambering from a cream/white to a more golden cream.
Red Oak: slight ambering of the pinkish tan coloration when freshly installed.
White Oak: slight muting of the color variation to a straw/medium brown color.
Walnut: medium degree of ambering from the darker chocolate brown when freshly laid, to a lighter brown color.
Cherry, Brazilian: pronounced darkening from tan/salmon color when freshly laid to deep reddish brown.
Chestnut, Southern: medium degree of darkening from a golden tan to more uniform nut brown
Cypress, Australian: slight muting of the color range and slight ambering over time
Mahogany, Royal: medium degree of darkening over time to a deeper reddish brown.
Mahogany, Santos: slight muting of the color range and slight darkening
Rosewood, Caribbean: medium degree of darkening and slight muting of the color range
Walnut, Caribbean: medium degree of muting of color range as well as darkening to medium brown with reddish tints.