Provide value-dependent color to \cellcolor command

Question

I would like to create a table-based heatmap. The answer https://tex.stackexchange.com/a/175035/70170 looks like what I need, but instead of three fixed colors, I'd like to call \cellcolor{} with a color dependent on the cell value.

Here's my attempt:

\documentclass{article}
\usepackage{colortbl}
\usepackage{pgfplots}
\begin{document}
\newcommand{\MinNumber}{6}%
\newcommand{\MidNumber}{8} %
\newcommand*{\MaxNumber}{14}%
\def\zz#1{%
  \ifdim #1 pt > \MidNumber pt
     \pgfmathparse{int(100((#1 - \MidNumber)/(\MaxNumber-\MidNumber)))} %
     \cellcolor{yellow!\pgfmathresult!red} 
  \else
     \pgfmathparse{int(100((\MidNumber - #1)/(\MidNumber-\MinNumber)))} %
     \cellcolor{green!\pgfmathresult!yellow} 
  \fi
#1}
\begin{table}[]
\begin{tabular}{ccc}
  \zz{6}  & \zz{7}  & \zz{8}  \
  \zz{9}  & \zz{10} & \zz{11} \
  \zz{12} & \zz{13} & \zz{14}
\end{tabular}
\end{table}
\end{document}

Unfortunately, this does not produce the expected gradient result, but only pure yellow or pure red cells. I printed the \pgfmathresult to check that the computation is correct, and also tried some hardcoded offset like yellow!20!red, which works as well.

I must be overlooking the obvious, but can't figure out what it is. Help from the TeX expert would be much appreciated - thank you!

Note that I am not looking for alternative approaches to creating heatmap tables, but for a way to fix the approach using \colortbl's \cellcolor.

Answer 1

\cellcolor should be (after expansion) the first item in the cell, with no unexpandable token before it.

You can use \fpeval:

\documentclass{article}
\usepackage[table]{xcolor}
\usepackage{pgfplots}
\ExplSyntaxOn
\NewExpandableDocumentCommand{\fpcompareTF}{mmm}
 {
  \fp_compare:nTF { #1 } { #2 } { #3 }
 }
\ExplSyntaxOff
\begin{document}
\newcommand{\MinNumber}{6}%
\newcommand{\MidNumber}{8} %
\newcommand*{\MaxNumber}{14}%
\newcommand{\zz}[1]{%
  \fpcompareTF{#1>\MidNumber}{%
    \cellcolor{%
      yellow!\fpeval{round(100((#1 - \MidNumber)/(\MaxNumber-\MidNumber)),0)}!red%
    }%
  }{%
    \cellcolor{%
      green!\fpeval{round(100((\MidNumber - #1)/(\MidNumber-\MinNumber)),0)}!yellow%
    }%
  }%
  #1%
}
\begin{table}[htp]
\begin{tabular}{ccc}
  \zz{6}  & \zz{7}  & \zz{8}  \
  \zz{9}  & \zz{10} & \zz{11} \
  \zz{12} & \zz{13} & \zz{14}
\end{tabular}
\end{table}
\end{document}