Can't wait for spring and a little rain.

Fur color in squirrels is controlled by the amount of melanin in their hair cells. This is true for many mammals. If they produce too much they can become very dark….almost to black. If they produce none or close to none they can become almost white. If they produce less than normal they can become blonde as the one pictured.

Very cool! I've never seen that in all my years.

Gunny456 said:

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Fur color in squirrels is controlled by the amount of melanin in their hair cells. This is true for many mammals. If they produce too much they can become very dark….almost to black. If they produce none or close to none they can become almost white. If they produce less than normal they can become blonde as the one pictured.

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Do they change over time or with the seasons?

When I was in Calgary we had white tail prairie hares that would be pure white in the winter and brown in the summer.

It was cool to watch them change during the spring and fall and be a mix of the two colors

Yes they can. Melanocytes are the pigment producing cells within the animal. These can be controlled by a genetic basis of developmental physiology or evolutionary physiology. The pelage (Color) that is controlled by a genetic basis is where the melanistic anomalies occur like solid white or solid black or variations thereof....in loose terms a genetic mutation, for lack of better terms. (Like the color of the squirrel) However, genetics can also insure normal physiology that causes the natural production of melatonin.
Examples of this for some mammals is when in the winter days get shorter which cause higher levels of melatonin which inhibit the production of prolactin leading to production of pure white winter fur to blend in with the snow. Conversely, when days get long again in spring and summer, melatonin decreases and the coats get color again to blend into the environment.
In some environments the shorter days will cause some mammals to have darker colors to help the animals absorb more heat for colder months and become lighter in hot months to reflect heat. Some researchers believe this is due to evolutionary changes of physiology rather than genetic.