I think any changes to the foreground colour during a game won't affect text that has already been printed, so if you wanted you could do this:
foreground <&H0080FF>
msg <Lots |xn>
foreground <&H8080FF>
msg <of |xn>
foreground <&HFF0080>
msg <pretty |xn>
foreground <&H80FF00>
msg <colours>
foreground <black>
No idea what that looks like as I'm not at a machine with Quest on it at the moment, but I think it should work.