The following gives an unexpected result:

(display (show #f (as-red (as-bold (as-underline "Hello!\n") "World!\n"))))

The color of "Hello!\n" is red, but the color of "World!\n" is white.

(The reference implementation uses an (undocumented) state variable
"color". I think it has to make use of two more state variables,
namely "underline?" and "bold?".)

Marc