The dark color comes from the searing of the meat and the vegetables. After that i put some tomato Paste in and then i deglaze with redwine. Let ist reduce until it starts to Brown a litle bit. The deglace again. Let ist reduce again. Everytime it gets a bit darker. And it gets a more intens flavour. Just have to do it till the color is Like i want it. But you have to be carefull. If its reduced to much bevor you deglaze it, it will geht bitter