If your administrator selected "Disable the selection of fully booked cells" in the Administration Settings you will not be able to select booked or overbooked Publication Dates.
Any user can turn this feature on by navigating to the Administration Setting and opening the Personal Settings or the Organization Settings. Please check the little checkbox "New Publication Date Calendar Media Configuration" Your administrator can set it for ALL users in your company.
Configure Cell Background Colors
This feature is using the same colors like the ones you have configured for your booking calendar. If you like to change the default please read more here: 18.104.22.168 Configure Cell Background Colors.
Additionally, you can change the detail view fields by modifying the values in the following feature setting record. Navigate to Feature Setting and search for Feature Name: NewMediaConfiguration.