% initial figure
pcolor(x,y,z)
shading flat
hold on
cbar = colorbar
caxis([-8 8])
set(cbar,'linewidth',2)
[C1,H1]=contour(x,y,z,[-8:1:-1],'k:');
[C2,H2]=contour(x,y,z,[1:8],'k-');
[C0,H0]=contour(x,y,z,[0 0],'k-');
set(H0,'lineWidth',2)
set(gca,'linewidth',3,'fontsize',14)
set(cbar,'fontsize',12);

% and changes
colormap('bone')
set(H1,'color','w','linestyle','-')
t1 = clabel(C1,H1);
set(t1,'color','w')
t2 = clabel(C2,H2);
t0 = clabel(C0,H0);