The Properties on the Notifier that a developer can modify are discussed here> Notifier
Properties
BackgroundColor
Specifies the background color for alerts (not dialogs).
NotifierLength
Specifies the length of time that the alert is shown – either “short” or “long”.
TextColor
Specifies the text color for alerts (not dialogs).
An extension might help. I don't know if there is one that allows that. At the present time, developers can not change the properties you want in the native Notifier dialogs. What you see are the default properties for the Android version in use.