Hi. I see you have set your Display Settings to use the “Full” styling, which by default looks like this.
The “Tribe Events” style by default looks like this.
You could use this custom CSS to make the text white:
body.tribe-events-style-full .tribe-events-calendar th {
color: #ffffff;
}
You can add custom CSS code via your child theme’s style.css file or via a plugin like Simple Custom CSS or, my favorite, Jetpack. Jetpack supports regular CSS and the LESS and Sass pre-processors.
If you’re not a CSS expert, Jetpack’s Custom Design reference may prove helpful.
Please let me know how it goes for you.