After a whole lot of research, I've found nothing that solves that excact problem. Allthough I ended up finding two solutions wich solves the issue of telling the individual bars from oneanother:
1) using legend:
b=bar(tvec_a(:,N),data_a,1);
title(name)
xlabel(X)
ylabel('Consumption')
axis([-inf inf -inf inf])
legend({'zone 1','zone 2', 'zone 3', 'zone 4'},'Location','northwest')
grid on

2) using bar labels
b=bar(tvec_a(:,N),data_a,1);
title(name)
xlabel(X)
ylabel('Consumption')
xtips1 = b(1).XEndPoints;
ytips1 = b(1).YEndPoints;
labels1 = 'z_1';
text(xtips1,ytips1,labels1,'HorizontalAlignment','center',...
'VerticalAlignment','top','color','w')
xtips2 = b(2).XEndPoints;
ytips2 = b(2).YEndPoints;
labels2 = 'z_2';
text(xtips2,ytips2,labels2,'HorizontalAlignment','center',...
'VerticalAlignment','top','color','w')
xtips3 = b(3).XEndPoints;
ytips3 = b(3).YEndPoints;
labels3 = 'z_2';
text(xtips3,ytips3,labels3,'HorizontalAlignment','center',...
'VerticalAlignment','top','color','w')
xtips4 = b(4).XEndPoints;
ytips4 = b(4).YEndPoints;
labels4 = 'z_2';
text(xtips4,ytips4,labels4,'HorizontalAlignment','center',...
'VerticalAlignment','top','color','w')
axis([-inf inf -inf inf])
grid on

I personally thinks the legend is the better sollution
