Colored underlining without affecting vertical spacing

Question

I'm using the coloured underlining trick described in the ulem package manual (p.3). The underlining looks good, but interacts poorly with align-like environments, where (in contrast to \uline) it affects the height of the row:

It is possible to have a version of \reduline that, modulo colour, behaves as \uline?

\documentclass{article}
\usepackage{amsmath}
\usepackage{ulem}
\usepackage{xcolor}

\newcommand\reduline{\bgroup\markoverwith{\textcolor{red}{\rule[-0.5ex]{2pt}{0.4pt}}}\ULon}

\begin{document}

\begin{align*}
  \uline{ABCD} + EFGH \\
  \reduline{ABCD} + EFGH \\
  ABCD + EFGH
\end{align*}
\end{document}

Answer 1

Well, this works....

\documentclass{article}
\usepackage{amsmath}
\usepackage{ulem}
\usepackage{xcolor}

\newcommand{\reduline}[1]{{\color{red}\uline{{\color{black}#1}}}}

\begin{document}

    \begin{align*}
    \uline{ABCD} + EFGH \\
    \reduline{ABCD} + EFGH \\
    ABCD + EFGH
    \end{align*}
\end{document}

Answer 2

Example:

\documentclass{article}
\usepackage{amsmath}
\usepackage{xcolor}
\usepackage{accents}


\newcommand{\redlb}[1]{{\color{red}\underaccent{\bar}{\color{black}#1}}}

\begin{document}

\begin{align*}
  {A} + B \\
  \redlb{A} + B \\
  A + B
\end{align*}
\end{document}

Your red under-bar is wider than mine. The author of the accents package questions the wisdom of using wide bars, but if you want one of those then you can find out as an answer to a different question how to accomplish that. Strangely, wide tildes are easier.

EDIT

And here's how to get a wide tilde under accent:

\documentclass{article}
\usepackage{amsmath}
\usepackage{xcolor}
\usepackage{accents}
\DeclareMathAccent{\wtilde}{\mathord}{largesymbols}{"65}

\newcommand{\redlb}[1]{{\color{red}\underaccent{\bar}{\color{black}#1}}}
\newcommand{\redwt}[1]{{\color{red}\underaccent{\wtilde}{\color{black}#1}}}

\begin{document}

\begin{align*}
  A + B \\
  \redlb{A} + B \\
  \redwt{A} + B
\end{align*}
\end{document}