Is it in full sun or part shade? In full sun many dark colored flowers fade especially if it is very hot and they are newly planted. The one that is not blooming doesn't have to make blooms at the same time as it is trying to settle in it's roots. Is there any way you can shade it during the hottest part of the day. Perhaps put a flower pot in front of it. Then make sure has enough moisture to keep the ground wet (but not sopping) around it's roots