Pinkie tip of tail.. is this normal?

[Kraykray]

By far the youngest one I've had, I have had it for 4 days and it could not of been more then 2 days old when it was found yesterday I noticed the tip of it's tail getting darker and was wondering if this is normal. First picture was the day it was found and the second is today.

[Kraykray]

By far the youngest one I've had, I have had it for 4 days and it could not of been more then 2 days old when it was found yesterday I noticed the tip of it's tail getting darker and was wondering if this is normal. First picture was the day it was found and the second is today. with pictures