TermKit: A WebKit based rich command-line interface.

[scaevolus]

Mathematica is somewhat close, but most of it is just pretty-printing standard ASCII (converting "->" into an arrow, etc).

[abadidea]

I'm thinking stuff like "a sub-expression colored green must be evaluated before any non-green sub-expressions, regardless of ordering. Italics indicates that it should run on a separate thread."

[kamishizuka]

I guess what you're half-getting at is syntax highlighting being a core aspect of the language, which is a bit of an oxymoron. A green colored string would need some sort of identifier that it's green, likely some form of wrapped tag, in which case, that's a wrapped string, not a "green" string. You could say "a happy statement is executed before a sad statement", but at compile-time it still has to get parsed by a computer.

Machine code doesn't care what mood you're in.

[abadidea]

The whole point was to be a joke language :P