Why have all the squirrels tails gone white?

For our two common backyard squirrels (the gray squirrel and the fox squirrel), it’s normal for growing squirrels to undergo a “spring molt.”

For gray squirrels, this typically involves slight change in color and follows a distinct head-to-tail pattern. (It’s described quite well on the Wild Adirondacks website.)

Since you mentioned that your squirrel is growing in to gray/white fur, our best guess is that it’s a juvenile gray squirrel growing into its adult colors.