documentclass{article}
usepackage{pgfkeys}

pgfkeys{%
  /path/.cd,
  color/.code=#1,
}

pgfkeys{/path/.cd,color=yellow} %typeset "yellow" as desired

pgfkeysvalueof{/path/color} %get nothing, typeset "yellow" is wanted

color{pgfkeys{/path/.cd,color=yellow}} %color{yellow} is desired,but fail to compile

end{document}