LaTeX: Hack for top-level color changes with dvipdfmx

bxdpx-tchack.sty

% bxdpx-tchack.sty
\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{bxdpx-tchack}[2023/07/01 v0.1]
\def\bxqcx@pkgname{bxdpx-tchack}
\ifx\currentgrouplevel\@undefined
  \PackageError\bxqcx@pkgname{e-TeX extension not supported}\@ehc
\expandafter\endgroup\fi\relax
\AtBeginDocument{%
  \def\bxqcx@org@set@color{\special{color pop}}
  \ifx\bxqcx@org@set@color\reset@color
    \set@color % push once
    \let\bxqcx@org@set@color\set@color
    \def\set@color{%
      \ifnum\currentgrouplevel>\z@ \bxqcx@org@set@color
      \else \special{color pop}\special{color push \current@color}%
      \fi}%
  \else
    \PackageError\bxqcx@pkgname{Unsupported color driver}\@ehc
  \fi}
%% EOF

sample-bxdpx-tchack.tex

% upLaTeX + dvipdfmx (essential)
\documentclass[dvipdfmx]{jsarticle}
\usepackage{xcolor}
\colorlet{R}{red}\colorlet{B}{blue}\colorlet{G}{green!50!black}
\usepackage{bxdpx-tchack}
\newcommand*\cS[1]{\color{#1}☃\color{black}}
\newcommand*\cNice[7]{%
  \cS{#1}っ\cS{#2}\cS{#3}\cS{#4}っ\cS{#5}っ　\cS{#6}っっ♪\cS{#7}っっ♪}
\newcommand*\cNicePar{%
  \cNice{R}{B}{R}{G}{B}{R}{R}　\cNice{B}{B}{G}{R}{G}{B}{B}\par
  \cNice{G}{R}{R}{R}{B}{G}{G}　\cNice{R}{G}{R}{B}{G}{R}{R}\par}
\begin{document}
\cNicePar \cNicePar \cNicePar \cNicePar \cNicePar
\end{document}