Nice! Great work on the details 
Did you try just using IonCard without IonCardContent? I only ever use IonCard by itself, never any of the card sub-components. I just tried, though, and the text is still gray. But, you can set the color by using the following:
ion-card {
--color: #000;
}
Unfortunately I don’t have a Mac to try. It could possibly be a bug in Apple’s web wrapper (WKWebView). Have you tried looking at DevTools for the app running in the simulator? Directions here.