Mark, I like the way this looks:
It's purple heart, red begonia, and the joseph's coat that you mentioned. I think that lime green is going to enhance all the colors
So I might look for the angelonia, lantana, and the chartreuse joseph's coat to put in the mailbox garden. And then carry over that chartreuse joseph's coat into my larger front walkway/porch area garden, along with the purple heart and the begonia.