How to Automatically Overlay a Title of a Different Color onto Itself

Question

I would like to be able to overlay a title of one color onto the same title of a different color to achieve a different effect; and I would like, if possible, to do this automatically without creating a special environment. (This is easy to do with, say, apspicture with two\rput commands)

Consider

\documentclass{book}
\usepackage{xcolor}
\definecolor{aqua}{RGB}{0, 188, 188}

\begin{document}
\thispagestyle{empty}
\Huge

\begin{center}
\textbf{\color{black}{HOW TO OVERLAY THIS TITLE}}

\textbf{\color{aqua}{HOW TO OVERLAY THIS TITLE}}

\vspace*{45pt}

{\textbf{\color{black}{HOW TO OVERLAY THIS TITLE}}}\\[-30pt]

{\textbf{\color{aqua}{HOW TO OVERLAY THIS TITLE}}}
\end{center}

\vspace*{35pt}

That is, how to do it \underline{\textit{automatically}}.
\end{document}   

which yields

In the MWE, I want to overlay the light aqua title over the black title---which I had accomplished by "trial and error" and inspection using a series of \\[] commands until I determined that \\[-30pt] seems to work.

But, I would like to know if there is a command of some sort that will do this automatically without invoking any special environment like pspicture, tikz, etc.? (Or is, perhaps, trial and error with negative vertical skips the (only) way for the usual document environment?)

Answer 1

This will work if the two versions are the exact same size. Otherwise you would have to overlay each letter separately.

\documentclass{article}
\usepackage{xcolor}
\definecolor{aqua}{RGB}{0, 188, 188}

\newcommand{\mytitle}[1]% #1 = title
{\bgroup
  \Huge
  \sbox0{\parbox{\columnwidth}{\centering\textbf{\color{black}#1}}}%
  \sbox1{\parbox{\columnwidth}{\centering\textbf{\color{aqua}#1}}}%
  \noindent\usebox0\llap{\raisebox{1pt}{\usebox1}}
\egroup}

\begin{document}
\mytitle{HOW TO OVERLAY THIS TITLE}
\end{document}

Answer 2

An easy way to do this is by letting LaTeX calculate the width of the box just written and then jump back horizontally, as shown here:

\documentclass{book}
\usepackage{xcolor}
\definecolor{aqua}{RGB}{0, 188, 188}

\newlength{\aqualength}
\newcommand{\aqualay}[1]{%
\bfseries%
\settowidth{\aqualength}{#1}%
\color{black}{#1}%
\hspace{-\aqualength}%
\color{aqua}{#1}%
}

\begin{document}
    \thispagestyle{empty}
    \Large
    \begin{center}      
        \aqualay{HOW TO OVERLAY THIS TITLE}
    \end{center}
\end{document}

The result is:

---

Using your vertical approach one would be able to use the negative \baselineskip:

\documentclass{book}
\usepackage{xcolor}
\definecolor{aqua}{RGB}{0, 188, 188}

\begin{document}
    \thispagestyle{empty}
    \Large
    
    \begin{center}
        \textbf{\color{black}{HOW TO OVERLAY THIS TITLE}}
        
        \textbf{\color{aqua}{HOW TO OVERLAY THIS TITLE}}
        
        \vspace*{45pt}
        
        {\textbf{\color{black}{HOW TO OVERLAY THIS TITLE}}}\\[-\baselineskip]
        
        {\textbf{\color{aqua}{HOW TO OVERLAY THIS TITLE}}}
    \end{center}
    
    \vspace*{35pt}
    
    That is, how to do it \underline{\textit{automatically}}.
\end{document}   

Answer 3

Another variant using the package xcoffins that allows the precise joining of boxes without guessing.

The command \OverlayTitle{color upper}{color back}{text}{x offset}{y offset} will typeset the overlay.

\documentclass{book}
\textwidth=6.5in
\usepackage{xcolor}
\definecolor{aqua}{RGB}{0, 188, 188}

\usepackage{xcoffins}
\NewCoffin\upperlayer
\NewCoffin\lowerlayer
\NewCoffin\framex
\newcommand{\OverlayTitle}[5]{% 
\SetHorizontalCoffin\upperlayer{\color{#1}#3}
\SetHorizontalCoffin\lowerlayer{\color{#2}#3}
\SetHorizontalCoffin\framex{}
\JoinCoffins*\framex[l,t]\lowerlayer[l,t]   
\JoinCoffins*\framex[l,t]\upperlayer[l,t](#4,#5)
\TypesetCoffin\framex   
}

\begin{document}
    \thispagestyle{empty}
    \Huge
    
    \OverlayTitle{aqua}{black}{HOW TO OVERLAY THIS TITLE}{-0.5pt}{0.5pt}    
    
    \bigskip
    
    \OverlayTitle{red}{black}{HOW TO OVERLAY THIS TITLE}{1pt}{1pt}  
    
\end{document}