SwiftUI seems to be incomplete compared to what is provided by UIColor. The primary and secondary refers to the text colors, which are the UIColor.label and UIColor.secondaryLabel.
A simple extension to provide more UIColor:
public extension Color {
static let lightText = Color(UIColor.lightText)
static let darkText = Color(UIColor.darkText)
static let label = Color(UIColor.label)
static let secondaryLabel = Color(UIColor.secondaryLabel)
static let tertiaryLabel = Color(UIColor.tertiaryLabel)
static let quaternaryLabel = Color(UIColor.quaternaryLabel)
static let systemBackground = Color(UIColor.systemBackground)
static let secondarySystemBackground = Color(UIColor.secondarySystemBackground)
static let tertiarySystemBackground = Color(UIColor.tertiarySystemBackground)
// There are more..
}
However, a huge drawback is that the colors will not automatically change between light & dark modes.
The above code is only for iOS, while macOS/AppKit does not have corresponding lightText etc.
Therefore, a better solution is to define such colors in Assets Catalog.