Jointing clinker bricks - different colors

About 2 weeks ago, the clinker slips on our house were grouted. Now I saw yesterday (in daylight) that the grout color is very different (see picture). How does something like this happen? Is the grouting contractor to blame?

Better ask the bricklayer, [Verfuger]. Maybe you have to wait for the upper area to dry. Maybe it is also a defect. The expert can tell you more, it is obvious after all. Regards