\documentclass[border=10pt]{standalone}
\usepackage{tikz}
\usepackage{fontspec}

\begin{document}
\begin{tikzpicture}

% Define dimensions
\def\boxsize{1.5}  % 1cm box size
\def\gap{0.5}   % 0.5mm gap between boxes
\setmainfont{Ubuntu}
\def\labelsize{7}  % Size for the labels
\pgfmathsetmacro{\gridsize}{(\boxsize + \gap)}

% Create 10x10 grid of boxes
\foreach \row in {0,...,9} {
    \foreach \col in {0,...,9} {
        % Calculate gray value (0 to 99)
        \pgfmathsetmacro{\grayval}{(100 - (\row * 10 + \col))}
        \pgfmathsetmacro{\grayscale}{(\grayval/100)}
        \pgfmathsetmacro{\graylabelraw}{1-\grayscale}
        \pgfmathprintnumberto[fixed,zerofill,precision=2,assume math mode]{\graylabelraw}{\graylabel}

        % Calculate position
        \pgfmathsetmacro{\x}{\col * \gridsize}
        \pgfmathsetmacro{\y}{9 - \row * \gridsize}  % Invert Y to start from top

        % Draw box using proper grayscale
        \draw [fill=black!\grayval]
            (\x, \y) rectangle ++ (\boxsize, -\boxsize);

        % Add label (white text for dark boxes, black for light ones)
        \pgfmathsetmacro{\textcolor}{ifthenelse(\grayval > 50, "white", "black")}
        \node[text=\textcolor] at (\x + 0.5*\boxsize, \y-0.2*\boxsize)
            {\fontsize{\labelsize}{\labelsize}\selectfont\graylabel};
    }
}

\end{tikzpicture}
\end{document}