Add color indicator in calendar to show dates volunteer is working

Our volunteers typically sign up for several opportunities at a time each month. They've been asking if there's a way to more easily see what days they're already working. I have a couple related ideas that would help with this.

First, in the calendar they can see dates that are available in green and dates that have a waitlist in yellow. Can we have another option to show dates they already have an opportunity scheduled in another color, perhaps blue?

Second, below the calendar, on a date that has opportunities available, all opportunities are listed, even ones the volunteer has already signed up for. Can there be some indicator there on events that the volunteer is already registered for? Otherwise they can't tell if they're already registered until the next screen after they try again to register themselves or add to waitlist.

Finally, and similar to #2 above, on the opportunity registration page there's also no indicator if the volunteer has already registered for the opportunity until after they try to register/waitlist for the opportunity again on the next page. This page also has the green/yellow color indicator when the opportunity is hovered over. It would be nice if there could be another color indicator for "already registered/waitlisted" and some other text indicator or prevention of going to the next screen.