How do I design a beautiful 6 month calendar view with 15+ event types?

I have designed a calendar web application at my work, and it has been well recieved. So well that multiple departments of my company has adapted it, and requested their own categories for their respective events. It has also been made available to our customers.

My problem is that what started out as a nice design, with four different colors, has turned in to an orgy of distracting colors, which frankly looks like someone puked up skittles (if skittles had 15 colors). I have tried multiple color schemes, but it always end up looking worse than it did. Here is the calendar as it looks now:

The idea is that all departments can select their relevant categories by choosing visibility from the menu on the left. But I would like the calendar to look good, even with all categories visible.

I tried to create a palette with 20 colors to choose from, but it ended up looking even worse. I'm starting to think that more colors might not be the best options, and that different options, like radial or striped colors, like here, might be the best option. I would however, very much like to get some examples or visualisations on options that might work. I'm also very much open to redesigning the whole table layout, like dropping the black border between columns and/or events.

I have tried finding good examples myself, but I could only find Google calendar-like month views, or empty six month calendar views for printing.

By the way, I am not expecting anyone to design this for me. I just have a feeling that somewhere out there, there are great examples or inspiration, and that I just haven't been able to find it myself.

UPDATE, TWO YEARS LATER:

I now have a brand new design. We accepted the fact that you cannot make this many colors work. Then we grouped the similar categories into a total of 7 colors, inkluding grey and white. Users can still select visibility of individual categories, but now it looks more professional, and less like unicorn barf.