Hello leland5,
We understand you have questions about reordering the colors for flagged mailboxes in macOS Mail. We'd like to provide you with some information on this.
Based off of the screenshot you provided, your flagged mailbox colors are appearing as expected with macOS Catalina. Here's more information on flagging emails: Flag emails in Mail on Mac.
As of right now there is no way to change the color order or reorganize those mailboxes the way you would with other types of mailboxes. You can leave feedback with Apple if this is something you would like to see added in future macOS versions. That feedback can be left here: Product Feedback.
Thanks for using Apple Support Communities.
Take care.