I’m jealous you got a picture of a fox at all, never mind a clear one: I’m sure they are around here (I hear them in the summer “barking”) but I’ve no photos and not seen all year.

However, you might want to try a little post-processing in whatever software you’ve got - it might be called a luminance histogram, tone curve or something like that, but it should address the rather washed out appearance without just darkening the entire shot. If you’ve a RAW format of the photo, work on that, but even a JPG might be improved.

Beautiful animal.

To add to the other poster’s advice, another good way to get better color saturation (i.e. less washed out colors) is simply to under-expose a bit. In my experience digital cameras always tend to over-expose, so you can usually just set them to underexpose a bit and all your pictures will look instantly better.