You can only change event colors by content type or taxonomy terms in Calendar view. More advanced coloring requires some programming.
Source code viewer
(function($){$().ready(function(){ $('div.view div.calendar-calendar td').each(function(){ // console.log($(this).attr('data-date')); sendDate = new Date(Date.parse($(this).attr('data-date'))) today = new Date(); today.setHours(0,0,0,0); // Past if (sendDate < today) { $(this).find('div.monthview, div.weekview, div.dayview').css('background', 'grey'); } // Future if (sendDate > today) { $(this).find('div.monthview, div.weekview, div.dayview').css('background', 'green'); } // Today if (sendDate == today) { $(this).find('div.monthview, div.weekview, div.dayview').css('background', 'red'); } }); });})(jQuery);Programming Language: Javascript