\documentclass{testsuite}
\usepackage{fontspec}
\usepackage{xcolor}
\begin{document}
   \fontspec[ SizeFeatures={
       {Size={-8}, Font=TeX Gyre Bonum Italic, Color=AA0000},
       {Size={8-14}, Color=00AA00},
       {Size={14-}, Color=0000AA}} ]{TeX Gyre Chorus}

   {\scriptsize Small\par} Normal size\par {\Large Large\par}
\end{document}