I blabbed my password in chat today. It's a weakness: a fullscreen not focused rdesktop can look focused. I typed happily away to discover with horror that my keystrokes went to the chat.
So I propose: Fullscreen not focused rdesktop should be dimmed!
If I had an 8-bit color display I could misuse the option -C: When the colors are wildly awry, I would see rdesktop to be out of focus.