Is the whole back of the neck colorized or is it in one place more than others? If it is closer to the heel it "might" be "posable" that moisture got into your neck pocket and some how leached some of the color [this is the only place I can think of that might have any dye that is exposed] down the neck. Or, is the inside of the case blue? How Much has your action moved? make a note of what it is now and check it in a while? Did you wipe down your bass when you felt the dampness?
Except for the moisture

, your climatising of your bass seems to be normal: bring in case, quickly open and close case, let sit for a half hour or so, then quickly check the inside or your case and if it is still to much of a difference re-close and let sit a while longer.