I think you would get what you need from the HTML::CalendarMonth module. I did quite a lot of work on a similar subject back along, and was lucky to receive the kind help of other monks. A node which might be the most relevant creates a calendar marked with the input dates can be found here. Otherwise a Super Search on HTML::CalendarMonth and Date::Calc would produce more information.

Good luck!

Update:There is a page of examples given by the author here. I'm not sure about placing text in the dates but even though I've never done it I'm sure it should be possible to provide different colours for the various members as you describe.