Something like this?
Rx = 1; %<-- Change these to make an ellipse instead
Ry = 1; %<-- Change these to make an ellipse instead
Rz = 1; %<-- Change these to make an ellipse instead
[X,Y,Z] = ndgrid(linspace(-Rx,Rx,50),linspace(-Ry,Ry,50),linspace(-Rz,Rz,50));
R = sqrt((X/Rx).^2 + (Y/Ry).^2 + (Z/Rz).^2);
seg = zeros(size(X));
seg(R <= 1 ) = 1;
seg(R <= 0.5) = 2;
slice(Y,X,Z,seg,0,0,0);
axis equal vis3d; colorbar;
