change background color of body (not a new email)

how can i use VBA to change the default color of white to some sort of gray? i am using darkmode and have changed the color of the menus and sidebars to gray but don't know how to change the default color of the body of an existing email.

note this is not pertaining to a New Email (where you CAN change the default colors) but to the outlook window itself

thanks

any help with this? :yes