How to plot 3D contour in real-time for the shortest time?

I need to plot 3D contour in real-time layer-by-layer. I got it already, that MATLAB does not have a standard function for 3D contour plot ( color = f(x,y,z) ), so I plot my graph dot-by-dot using a 'scatter3' function like this:

X = 10; Y = 20; Z = 50;
c = cell(X,Y,Z);

for i = 1:X
    for j = 1:Y
        for k = 1:Z
            c{i,j,k} = [(i-1)/X (j-1)/Y (k-1)/Z randi(5)];
        end
    end
end

zcount = 2;
figure

while zcount <= Z
    
    cla;
    
    for k = 1:zcount
        for i = 1:X
            for j = 1:Y
                clr = clrdet(c{i,j,k}(4));
                scatter3(c{i,j,k}(1),c{i,j,k}(2),c{i,j,k}(3),...
                    'MarkerFaceColor',clr,'MarkerEdgeColor',clr);
                drawnow;
                hold on;
                axis equal;
                grid on;
            end
        end        
    end
    
    zcount = zcount + 1;
    
end

function res = clrdet(int)
    switch int
        case 1
            res = 'r';
        case 2
            res = 'g';
        case 3
            res = 'b';
        case 4
            res = 'c';
        case 5
            res = 'm';
        otherwise
            res = 'k';
    end
end

The execution of my code takes a lot of time (about 0.5 sec a layer), when the whole contour should be plot in less than 0.4 seconds. Can you, please, suggest me, how to speed up my code? Maybe there is a way to plot 2D contour (XY section) on 3D graph?