The relevant portion of memoir.cls for the title is
\newcommand{\@maketitle}{%
\let\footnote\@mem@titlefootkill
\ifdim\pagetotal>\z@
\newpage
\fi
\null
\vskip 2em%
\vspace*{\droptitle}
\maketitlehooka
{\@bspretitle \@title \@bsposttitle}
\maketitlehookb
{\@bspreauthor \@author \@bspostauthor}
\maketitlehookc
{\@bspredate \@date \@bspostdate}
\maketitlehookd
\par
\vskip 1.5em}
As such, \maketitlehookd is basically the last thing, which should be on the first titlepage. A \clearpage after this hook should do, but is not the best solution. If there is more content on the first page, such that the content of the hooks go to the 2nd page, the clearpage should be there, but in this sense, the 2nd page is still a titlepage and should be in the same colour, in my point of view. Patching the end of \@maketitle is perhaps the better way.
\documentclass{memoir}
\usepackage{lipsum}
\usepackage{xcolor}
\usepackage{pagecolor}
\usepackage{xpatch}
% Patching the end of `\@maketitle` -- Assume that nothing is on the second page.
\xpatchcmd{\@maketitle}{\par
\vskip 1.5em}{%
\par
\vskip 1.5em
\clearpage\newpagecolor{white}}{}{}%
\title{Test}
\begin{document}
\newpagecolor{red}
\begin{titlingpage}
\maketitle
\end{titlingpage}
\newpagecolor{white}
\chapter{First chapter}
\lipsum[1]
\end{document}

titlingpage? It would be much easier then. – Apr 27 '15 at 14:15titlingpageenvironment. flav's answer used\maketitleon its own, but either way,aftepagewas what I was looking for. Thanks for your behind-the-scenes solution though. Might come in handy for other problems. – jkeirstead Apr 27 '15 at 17:08