I posted my system info in a private reply. I have tried playing with the customization in the Appearance menu, but it seems that I can only change the color of the entire table as a whole (including the lines), and not just the bar that includes the day number. Ideally I’d like to keep the lines a lighter/brighter color, and just make the background behind the day number a darker color. If that’s not possible, I can probably find a middle ground that allows the numbers to be visible over the background color, AND the month’s border lines be visible over my background image.
Thank you for pointing out that there are customization options in the Appearance menu though, I didn’t even know that was there. I thought the only options were in the “Options” section of the plugin itself.