On iOS: tap the share button in browser => add to home screen
On Android: tap the 3 dot menu button in browser => tap “install” or “add to home screen”
Surprisingly, those particular features aren’t locked behind premium. As for the top bar color, you might be able to change the theme in Lemmy/kbin itself in your profile settings to one that suits what you’re looking for. Unless you mean in Hermit itself. In that case, I’m not sure - I use it frameless.