If I remove the textcolor specification (and the corresponding 2 curly braces), the useless space around "someItem" disappears.
If I replace the "\begin{itemize} ... \end{itemize}" bloc by just a text, the useless space around "someItem" disappears.
Why are there these differences? I tried to remove all the blanks in my LaTeX source, because I thought there were causing some problems, but that didn't help.
Is it related to the notion of "vertical mode" (that I don't understand yet, but someone mentioned it in one my other posts about unwanted spaces)?
I saw some posts with similar problems (for example: Why does tcolorbox adds vertical space?), maybe their solution would work, but I still wouldn't understand what textcolor or itemize are breaking in my MWE...
I'm using LuaLaTex, but the result in the same on this online service: https://latex.net/texlive/
In fact, I don't really need a color for my text. I just put it to play with fonts in one of my documents. So I'll just remove the "textcolor" and my document will be ok, but I would still like to understand what's going on!
\documentclass{article}%
\usepackage{tcolorbox}%
\usepackage{enumitem}%
\begin{document}%
\begin{tcolorbox}[notitle]%
{\textcolor{blue}{%
\begin{itemize}%
\item{someItem}%
\end{itemize}%
}}%
\end{tcolorbox}%
\end{document}%