I may have a solution to your problem with Cortana.
To return Cortana to her natural darker colour, enable the setting "Dark Mode".
To enable this, go to Settings, -> Personalisation -> Colours -> (Scroll Down) -> Dark Mode.
You can disable this setting at any time.
I hope I have helped resolve your problem.
738 people were helped by this reply·
Did this solve your problem?
Sorry this didn't help.
Great! Thanks for marking this as the answer.
How satisfied are you with this reply?
Thanks for your feedback, it helps us improve the site.
How satisfied are you with this response?
Thanks for your feedback.