게시글이 올라온 것을 보고 한참 답변글을 작성하다가 submit 버튼을 눌렀더니 그런 글이 없다네요.

분한 마음에(^^) hoze님의 블로그를 찾아가서 같은 주제의 새 포스팅을 보고 간략히 답변을 답니다.

%!TEX program = lualatex
\documentclass{article}
\usepackage{luacode}
\usepackage[svgnames]{xcolor}

\newcommand*\myHighlight[1]{\textcolor{blue}{\itshape #1}}
\newcommand*\dream[1]{\textcolor{SeaGreen}{\bfseries #1}}
\begin{luacode}
function Replace_some_words ( s )
	s = s:gsub ( "([^\\])freedom", "%1\\myHighlight{freedom}" )
	s = s:gsub ( "([^\\])dream", "%1\\myHighlight{dream}" )
	s = s:gsub ( "([^in\\])justice", "%1\\myHighlight{justice}" )
	return s
end
\end{luacode}

\luaexec{
	luatexbase.add_to_callback ("process_input_buffer", Replace_some_words, "justice_justice")
}

\begin{document}

I have a dream.

It is obvious today that \dream{America} has defaulted on this promissory note, insofar as 
her citizens of color are concerned.
Instead of honoring this sacred obligation, America has given the Negro people a bad check, 
a check which has come back marked insufficient funds.
But we refuse to believe that the bank of justice is bankrupt.

We refuse to believe that there are insufficient funds in the great vaults of opportunity 
of this nation.
And so, we've come to cash this check, a check that will give us upon demand the riches of 
freedom and the security of justice.
We have also come to this hallowed spot to remind America of the fierce urgency of now.
This is no time to engage in the luxury of cooling off or to take the tranquilizing drug 
of gradualism.

Now is the time to make real the promises of democracy.
Now is the time to rise from the \dream{dark and desolate valley of segregation} to the 
sunlit path of racial justice.
Now is the time to lift our nation from the quicksands of racial injustice to the solid 
rock of brotherhood.
Now is the time to make justice a reality for all of God's children.

\end{document}

코멘트를 작성하려 한 이유는 만약에 \dream이라는 매크로가 있을 경우에 어떻게 할 것인가라는 생각 때문이었습니다.