Only one field is allowed for the legend field well. You may be trying to pack too much information into a single visual. Could you provide a small table visual alongside your current chart listing the dates in context and what their type is? Slicing to e.g. a month or a week would filter that table down. Clicking on a specific date in the existing chart would give you just that date's attributes in the table.
This chart + detail table is an idiom I use pretty frequently. Visuals are exceptional for spotting trends and relative proportions, and can hold an incredible density of data if used properly. At a certain point, though, information density becomes a negative.
This is all very subjective, but I hope these thoughts help you in designing effective reports for your organization. I realize I've not really given a self-contained satisfying answer here, and for that I apologize.
