Events Calendar in Phone View

I have an events page with a standard Squarespace calendar on it. When viewed on a desktop the tiles display the images that I have chosen, however, when viewed on a tablet or a phone the tiles just show a darker shade of grey. Is there a way that I can colour code the events (by category if possible) so that even if the image doesn't show the category of the event will be apparent. 

Thank you in advance for any helpful advice.