%needs a fontloader 2017-08-18 or later **and** a luatex 1.06!!!

% !Mode:: "TeX:UTF-8:Main"
%needs a fontloader 2017-08-18 or later **and** a luatex 1.06!!!

\documentclass{article}

\directlua{fonts.handlers.otf.registerpalette("demo", {
{ g = 0 },
{ g = 0.5, b=0, r=1 },
{ r = 1 },
{ r = 0, b= 1, g= 0},
}
)}

\begin{document}
\font\Emoj={file:seguiemj.ttf:mode=node;colr=yes;}
\Emoj \char"2661 \char"1F34D \char"1F986

\font\Emoj={file:seguiemj.ttf:mode=node;colr=demo;}
\Emoj \char"2661 \char"1F34D \char"1F986

\font\cow={file:koeielettersot.ttf:mode=node;colr=demo;} at 30pt
\cow ABC

\end{document}