how do i make email appear red in when delivered to a mailbox?

[Gordon]

Please use this BIG WHITE SPACE to write your question.
Thank you.

You failed to tell us your Outlook version, so I'll guess at
Tools-Organize-Using colours.

 

[Vince Averello [MVP - Outlook]]

I think that's a client side thing. Not sure if you can send something that
will be forced that way

 

[Brian Tillman]

<nothing>

You as sender cannot affect the presentation in the recipient's client.