hello Andrew
one solution is to overlay two mesh plots and ask for the second to have a single bright color (here red)
either only the mesh is red but you can also have plain (face) color as shown in the second example :
[X,Y] = meshgrid(-15:.5:15);
R = sqrt(X.^2 + Y.^2) + eps;
Z = sin(R).*R;
[m,n] = size(Z);
% create inner flat square
ind = round(m/2) + (-10:10);
Z(ind,ind) = 0;
figure
mesh(X,Y,Z)
hold on
m = mesh(X(ind,ind),Y(ind,ind),Z(ind,ind));
set(m,'Edgecolor','r');
% set(m,'Facecolor','r');
view(-30,75)
hold off
figure
mesh(X,Y,Z)
hold on
m = mesh(X(ind,ind),Y(ind,ind),Z(ind,ind));
set(m,'Edgecolor','r');
set(m,'Facecolor','r');
view(-30,75)
hold off
