The initial value that is shown in the URL field is a placeholder to provide an example of the URL that is expected. All fields that do not have focus do have a light bluish color background. But once a field has focus the field should turn white. Additionally, once you start typing in place of the placeholder that example value should disappear.
What browser are you using? If your using an unsupported browser  you could see unexpected behavior.
Assuming the browser version is good, you might also try clearing your browser cache to ensure it's not picking up old styles from a previous NiFi version you may have used.
Feel free to respond with some screenshots if these don't help.