A example below is based on xcolor and its convenient definition of gradients. The macro \vcellcolor calculates a step for a gradient given a value of a cell.

I also used a upper threshold where everything beyond gets the same representation as the highest value because there is not much between 1200 and 2700. Here's the outcome

\documentclass[11pt]{report}
\usepackage{array}
\usepackage{xcolor}
\usepackage{colortbl}
\usepackage{collcell}

\definecolorseries{lower}{rgb}{last}{cyan}{green!50}
\definecolorseries{higher}{rgb}{last}{green!50}{red!50}
\resetcolorseries[10]{lower}
\resetcolorseries[10]{higher}
\newcommand\vcellcolor[1]{%
    \centering
    \ifdim#1pt=200pt\cellcolor{lower!![0]}%
    \else%
      \ifdim#1pt>200pt%
        \ifdim#1pt>1200pt\cellcolor{red!50}%
        \else%
          \cellcolor{higher!![\fpeval{round(10*(#1-200)/1000)}]}
        \fi%
      \else%
        \cellcolor{lower!![\fpeval{round(10*#1/200)}]}
      \fi
    \fi #1}
\newcolumntype{C}[1]{%
    >{\collectcell\vcellcolor}wc{#1}<{\endcollectcell}}


\begin{document}
\begin{table}[tbh]
    \small
    \centering
    \begin{tabular}{wc{1cm} wc{1.5cm} *9{wc{0.5cm}}}
        \hline
        GN 491- &
        \begin{tabular}[c]{@{}c@{}}
            Fx {[}N{]}  / \\
            Hebel {[}mm{]}
        \end{tabular}
                  &  500 & 450 & 400 & 350 & 300 & 250 & 200 & 150 & 100
    \end{tabular}
    \par
    \begin{tabular}{wc{1cm} C{1.5cm} *9{C{0.5cm}}}
        \hline
        18 &  425 &  170 & 153 & 136 & 119 & 102 &  85 &  68 &  51 &  34 \\
        30 &  850 &  340 & 306 & 272 & 238 & 204 & 170 & 136 & 102 &  68 \\
        40 & 1100 &  440 & 396 & 352 & 308 & 264 & 220 & 176 & 132 &  88 \\
        50 & 1900 &  760 & 684 & 608 & 532 & 456 & 380 & 304 & 228 & 152 \\
        60 & 2700 & 1080 & 972 & 864 & 756 & 648 & 540 & 432 & 324 & 216 \\
        \hline 
    \end{tabular}
    \caption{A}\label{tab:my-table} 
\end{table}
\end{document}