Drone Configuration Background Coloring

I am running SpamSieve on a headless Mini in a drone configuration with Apple Mail. There are two mail accounts, and there is one Spam mailbox for both on the IMAP server.

The setup works great, except for one problem. The messages in the Spam mailbox (on all machines except the Mini) suffer from the Apple Mail induced low-contrast burnt-orange background color that makes them hard to read. Because these machines aren’t running SpamSieve, I don’t see a way to remove this background coloration. Can anyone help?