Hi Nick,
Thanks for reaching out!
Try adding this to your custom CSS area under Appearance > Customize (if your theme provides one) or to the style.css file in your child theme, replacing the #000000 with the color you would like to use:
.tribe-events-page-template #page #tribe-events-content-wrapper #tribe-events-content .tribe-events-calendar td {
background-color: #000000 !important;
}
If you would like a different color for past days, you can add this as well:
.tribe-events-page-template #page #tribe-events-content-wrapper #tribe-events-content .tribe-events-calendar td .tribe-events-past {
background-color: #000000 !important;
}
I hope that helps! Please let me know if you have any other questions.
Thanks,
Jennifer