forwardref.sty

\NeedsTeXFormat{LaTeX2e}
\ProvidesPackage{forwardref}[2015/08/10 Detect forward references]

\makeatletter

\usepackage{auxhook}
\newcounter{labelknownref}
\renewcommand*{\thelabelknownref}{\the\value{labelknownref}}

\AddLineBeginAux{%
  \string\providecommand\string\LabelKnown[2]{}%
}
\newcommand*{\LabelKnown}[2]{%
  \expandafter\xdef\csname lkr@#2\endcsname{%
    \@ifundefined{r@#1}{0}{1}%
  }%
}
% \usepackage{nameref}% load it now, because it redefines \ref
\AtBeginDocument{%
  \LetLtxMacro\myorgref\ref
  \DeclareRobustCommand*{\ref}[1]{%
    \begingroup
      \stepcounter{labelknownref}%
      \if@filesw
        \protected@write\@auxout{}{%
          \string\LabelKnown{#1}{\thelabelknownref}%
        }%
      \fi 
      \if\csname lkr@\thelabelknownref\endcsname 1%
        \hypersetup{linkcolor=blue}%
        \myorgref{#1}%
      \else
        \if\csname lkr@\thelabelknownref\endcsname 0%
          \hypersetup{linkcolor=red}%
          \myorgref{#1}\textsuperscript{\textcolor{red}{(forward reference!)}}%
        \else
          \hypersetup{linkcolor=orange}%
          \myorgref{#1}\textsuperscript{\textcolor{orange}{(unknown)}}%
        \fi
      \fi  
    \endgroup
  }%
}   

\makeatother