Howdy James!
That’s a cool idea. It certainly seems possible to create. You could give each venue it’s own unique CSS class, something like “.venue-venuenamehere” and then assign it a color via CSS. You would likely just need to create a theme override for any views that you have enabled on your calendar, such as List, Month, etc.
There would be a work around to make this happen without the need to write one line of code. You could try out the community addon, Events Category Colors. If you created a category for each venue, and then assigned all events in the venue to that category, then you could colorize everything with great ease!
Did that all make sense, or can I elaborate any? Would one of those solutions works?
Cheers!
– Brook