documentclass{minimal}
usepackage{tikz}
usetikzlibrary{matrix}

begin{document}
    begin{tikzpicture}
        defx{2}
    defy{2}
    defz{3}
    defyscale{0.850000}
    defzslant{1.000000}
    defxlab{x}
    defylab{y}
    defzlab{z}
    defgridcol{black!80}
    defshadecolA{white}
    defshadecolB{black!20}
    tikzset{
        grid matrix/.style={
            nodes in empty cells,
            matrix of nodes,
            column sep=-pgflinewidth, row sep=-pgflinewidth,
            nodes={
                rectangle,
                draw=gray,
                minimum height=1cm,
                anchor=center,
                align=center,
                text width=1cm,
                text height=2ex,
                text depth=0.5ex,
                inner sep=0pt,
                outer sep=0pt,
            }
        },
        grid matrix/.default=1.2em
    }

    begin{scope}

    % top matrix
    begin{scope}[transform canvas={xslant=zslant, yscale=yscale, shift={(-0.5*z, 0.5 * x)}, },transform shape]
    draw[color=black, thick, ] (-0.5* z,-0.5* x) rectangle (0.5* z, 0.5* x);
    shade[bottom color=shadecolA, top color=shadecolB] (-0.5* z,-0.5* x) rectangle (0.5* z, 0.5* x);

    matrix (top) [grid matrix]{
        |[fill=none]| 4 & |[fill=none]| 8 & |[fill=none]| 12 \
        |[fill=none]| 2 & |[fill=none]| 4 & |[fill=green]| 6 \
    };
    node [above, rotate=90, text width=x * 1cm, align=center] at (top.west) {xlab};
    end{scope}

    % front matrix
    begin{scope}[shift={(-0.5*z, -0.5 * y)}]
    draw[color=black, thick, fill=shadecolA] (-0.5* z,-0.5* y) rectangle (0.5* z, 0.5* y);
    %shade[left color=gray!10, right color=black!60] (-0.5* z,-0.5* y) rectangle (0.5* z, 0.5* y);

    matrix (front) [grid matrix]{
        |[fill=none]| 1 & |[fill=none]| 2 & |[fill=green]| 3 \
        |[fill=red]| 1 & |[fill=red]| 2 & |[fill=red]| 3 \
    };
    node [below, text width=z * 1cm, align=center] at (front.south) {zlab};
    node [above, rotate=90, text width=y * 1cm, align=center] at (front.west) {ylab};
    end{scope}

    % side matrix
    begin{scope}[transform canvas={yslant=1/zslant, xscale=yscale*zslant, shift={(0.5*x,-0.5*y)}, },transform shape]
    draw[color=black, thick] (-0.5* x,-0.5* y) rectangle (0.5* x, 0.5* y);
    shade[left color=shadecolA, right color=shadecolB] (-0.5* x,-0.5* y) rectangle (0.5* x, 0.5* y);

    matrix (side) [grid matrix]{
        |[fill=green]| 1 & |[fill=none]| 2 \
        |[fill=red]| 3 & |[fill=red]| 4 \
    };
    end{scope}
    end{scope}

    end{tikzpicture}
end{document}