Why is an extra page inserted before the cover page when changing page colors for a single page?

Question

I am using R and the knitr package to produce a LaTeX PDF. As the MWE below demonstrates, an extra, blank page is created before my boxed page, which is to be the cover of a book.

If I remove the final \\ after the Release 1.0 line, the extra page disappears. But this seems a hacky solution. More important, the same change did not fix the problem in my longer document.

I would very much appreciate finding out what I am doing wrong.

EDIT: AT DAVID Carlisle's suggestion, I hope this is the tex:

\documentclass{book}
\usepackage{graphicx}
\usepackage{color}
%% maxwidth is the original width if it is less than linewidth
%% otherwise use linewidth (to make sure the graphics do not exceed the margin)
\makeatletter
\def\maxwidth{ %
  \ifdim\Gin@nat@width>\linewidth
    \linewidth
  \else
    \Gin@nat@width
  \fi
}
\makeatother
\definecolor{fgcolor}{rgb}{0.345, 0.345, 0.345}
\newcommand{\hlnum}[1]{\textcolor[rgb]{0.686,0.059,0.569}{#1}}%
\newcommand{\hlstr}[1]{\textcolor[rgb]{0.192,0.494,0.8}{#1}}%
\newcommand{\hlcom}[1]{\textcolor[rgb]{0.678,0.584,0.686}{\textit{#1}}}%
\newcommand{\hlopt}[1]{\textcolor[rgb]{0,0,0}{#1}}%
\newcommand{\hlstd}[1]{\textcolor[rgb]{0.345,0.345,0.345}{#1}}%
\newcommand{\hlkwa}[1]{\textcolor[rgb]{0.161,0.373,0.58}{\textbf{#1}}}%
\newcommand{\hlkwb}[1]{\textcolor[rgb]{0.69,0.353,0.396}{#1}}%
\newcommand{\hlkwc}[1]{\textcolor[rgb]{0.333,0.667,0.333}{#1}}%
\newcommand{\hlkwd}[1]{\textcolor[rgb]{0.737,0.353,0.396}{\textbf{#1}}}%
\let\hlipl\hlkwb
\usepackage{framed}
\makeatletter
\newenvironment{kframe}{%
 \def\at@end@of@kframe{}%
 \ifinner\ifhmode%
  \def\at@end@of@kframe{\end{minipage}}%
  \begin{minipage}{\columnwidth}%
 \fi\fi%
 \def\FrameCommand##1{\hskip\@totalleftmargin \hskip-\fboxsep
 \colorbox{shadecolor}{##1}\hskip-\fboxsep
     % There is no \\@totalrightmargin, so:
     \hskip-\linewidth \hskip-\@totalleftmargin \hskip\columnwidth}%
 \MakeFramed {\advance\hsize-\width
   \@totalleftmargin\z@ \linewidth\hsize
   \@setminipage}}%
 {\par\unskip\endMakeFramed%
 \at@end@of@kframe}
\makeatother
\definecolor{shadecolor}{rgb}{.97, .97, .97}
\definecolor{messagecolor}{rgb}{0, 0, 0}
\definecolor{warningcolor}{rgb}{1, 0, 1}
\definecolor{errorcolor}{rgb}{1, 0, 0}
\newenvironment{knitrout}{}{} % an empty environment to be redefined in TeX
\usepackage{alltt}   
\usepackage[margin = 0.8in]{geometry}
\usepackage{afterpage}  % if coloring only one page, like the cover, use this at end
% https://tex.stackexchange.com/questions/25137/how-to-change-the-background-color-only-for-the-current-page
\usepackage{pagecolor}
\usepackage{xcolor}
\definecolor{lm_green}{RGB}{120, 162, 47}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\IfFileExists{upquote.sty}{\usepackage{upquote}}{}
\begin{document}
\newpagecolor{blue}
\thispagestyle{empty}    % removes header and page number on this page; like Excel Diff page number

\colorbox{lm_green}{                            
    \parbox[c]{0.98\linewidth}{
        \fontsize{65pt}{80pt}\selectfont             
        \vspace*{2in}                          
        \textcolor{white}{Data Graphs for Legal Management} \hspace{.3in} \\           
        \textcolor{white}{A competitive advantage for decisions} \hspace{.3in} \\
    \vspace*{1in}                                
    \textcolor{white}{\LARGE Rees W. Morrison, Esq.} \hspace{.3in} \\  %\large does not take an argument, re Carlisle
   %\vspace*{.1in}  
   \textcolor{white}{\LARGE Release 1.0} \\ 
   %\hfill \\
\par    
    }
}

\vspace*{2in}

\clearpage

\restorepagecolor

\end{document}

2.

\documentclass{book}   
\usepackage[margin = 0.8in]{geometry}
\usepackage{afterpage}  % if coloring only one page, like the cover, use this at end
% https://tex.stackexchange.com/questions/25137/how-to-change-the-background-color-only-for-the-current-page
\usepackage{pagecolor}
\usepackage{xcolor}
\definecolor{lm_green}{RGB}{120, 162, 47}
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
\begin{document}
\newpagecolor{blue}
\thispagestyle{empty}    % removes header and page number on this page; like Excel Diff page number
\colorbox{lm_green}{                            
    \parbox[c]{0.98\linewidth}{
        \fontsize{65pt}{80pt}\selectfont             
        \vspace*{2in}                          
        \textcolor{white}{Data Graphs} \hspace{.3in} \\           
        \textcolor{white}{A competitive advantage for decisions} \hspace{.3in} \\
    \vspace*{1in}                                
    \textcolor{white}{\LARGE{Confused by LaTeX}} \hspace{.3in} \\
   %\vspace*{.1in}  
   \textcolor{white}{\LARGE{Release 1.0}} \\ 
   %\hfill \\
\par    
    }
}

\vspace*{2in}

\clearpage

\restorepagecolor

<<setup, echo = FALSE, message = FALSE, cache = FALSE>>=
source("C:/Users/Rees/Documents/R/Scripts/gcm.R") 
opts_chunk$set(echo=F, warning=F, message=F, cache=T, fig.align='center', comment=NA)
@

\end{document}