It seems that in order to change the font color of all the text displayed in the graph, we cannot simply adjust it without changing the selected theme. In my case, with a dark background color, I wanted all the text within the graph to appear in white. To achieve this, a different theme needs to be imported instead of solely attempting to modify the font-color property. You can obtain the dark theme from the following link:
After downloading the library, include it in your script like so:
<script src="https://www.amcharts.com/lib/4/themes/dark.js"></script>
Subsequently, alongside the animated.js theme, invoke the dark theme as shown below:
am4core.useTheme(am4themes_dark);
am4core.useTheme(am4themes_animated);
Upon executing these steps, all text will appear in white along with the grid lines.