How to change the color profile of the OS X login screen?
I just solved it!

SOLUTION:

1.
Activate the OS X Root User in the System Preferences.

How to activate the root user: http://support.apple.com/kb/ht1528

2.
After the root user is activated, log out from your account and log in as the user "root". 

Go to System Preferences -> Displays -> Color and pick the color profile (that you want on your OS X Login Screen).

Log out of the Root Account and you'll see the selected color profile will be used on the Login Screen.

3.
Log back in to your normal account.

Now you can deactivate the root user via System Preferences, the same way it was activated.

The color profile selected via root user earlier will stay.

Result:
The color doesn't change anymore between Login Screen and account and I don't have a yellow/dark login screen anymore, finally!

Could Apple make that easier? YES!
But that's a pretty fast way to do it, without any "hacking" tricks.