\documentclass{article}
\usepackage[olddefault]{fontsetup}
\usepackage{luacolor}
\pagestyle{empty}
\newfontfamily{\ncmtest}[Renderer=Harfbuzz]{NewCM10-Regular.otf}

\definecolor{orange}{RGB}{255,191,0}

\definecolor{colorone}{RGB}{91,0,250}
\definecolor{colortwo}{RGB}{250,0,121}
\definecolor{colorthree}{RGB}{0,204,250}
\definecolor{colorfour}{RGB}{14,250,0}
\definecolor{colorfive}{RGB}{255,150,0}
\definecolor{colorgray}{gray}{0.8}

\newcommand{\emptydiacritic}{\char"034F}

\begin{document}
\Huge
{\ncmtest \color{colorgray}a\color{colorfour}̖\color{colortwo}̗\emptydiacritic\color{colorthree}́\color{colorone}̀\color{colorfive}̐}
\end{document}