UnScramble this Word: b o o t f a h t?

Questions

in mirc, what colour does control-4 give?

in motor racing, what is yellow?

in music, instrumental introduction to an opera or other musical or nonmusical dramatic work?

in music, the art of extemporization or creating all or part of a composition at the moment of performance?

in musical notation, what is the term for the symbol at the beginning of a staff?