In some behind the scenes work for spacing reasons, the pieces of a syllable get split up in gregoriotex and then reassembled for printing. Normally this works fine, but we're running into some ligature problems when styling is involved. The results can be seen in the following MWE:
\documentclass{article}
\usepackage{xcolor}
\begin{document}
\Huge
{\color{red}f}{\color{red}i}
{\color{red}fi}
{\itshape f}{\itshape i}
{\itshape fi}
\end{document}
In the first example, the fact that the "f" and the "i" have color applied to them separately, the ligature (shown in the second line) between them doesn't show (even though the color is the same). On the other hand, this doesn't happen for \itshape. Is there a way for the color example to work more like the italics example?
LuaTeX tag is used because the gregoriotex package (into which any solution is destined to be inserted) is only compatible with Lua(La)TeX.
