This article explains why some courses are grayed out.

Whenever you see a grayed out course in the My Courses widget, it means you are enrolled in a course that has not yet started. You will be unable to click on the course or open the course.

The course will automatically open and change to colours, when the start date has passed. In case the course is still grayed out when your first lectures have started, check with your instructor if this is intentional or if there has been a mistake with the settings.