The Events Calendar Category Colors: place this code in your theme's functions.php file if you see the calendar taking on the styling of the first event of the month. If it causes problems. Don't use it.

remove_tribe_cat_once.php

// Try to stop the first event category from being added to the article classes
// (when the default page template is used) - Thanks Barry
add_filter('post_class', 'remove_tribe_cat_once', 1);

function remove_tribe_cat_once(array $classes) {
	if ( class_exists('TribeEvents') ) {
		// The Main Calendar Page or Calendar Category Page
		if (( tribe_is_month() && !is_tax() ) || ( tribe_is_month() && is_tax() )) { 
			static $count = 0;
			if ($count++ === 0) {
				remove_filter('post_class', array(TribeEvents::instance(), 'post_class'));
			}
			else {
				add_filter('post_class', array(TribeEvents::instance(), 'post_class'));
				remove_filter('post_class', 'remove_tribe_cat_once');
			}
			return $classes;
		}
	}
}