[Xy-pic] Color option help needed

[Michael Barr]

Assume my preamble contains the lines
\input xy
\xyoption{arrow}
\xyoption{color}
\UseCrayolaColors
Where can I place [red] in the line
  $$\xy \ar@{->}^{f}(20,0) \endxy$$
to generate a red arrow with a black f?

While I am at it, why can't I say \xyoption[arrow,color] without getting 
an error message that "arrow," is not a valid option?

Michael


-- 
        Every gun that is made, every warship launched, every rocket fired
signifies, in the final sense, a theft from those who hunger and are not
fed, those who are cold and are not clothed. -Dwight D. Eisenhower