Why this enum is strange?

Using Swift
10

This is a bit odd limitation that standard colours like red, green, etc are not available via Color(systemName:). Here's a possible workaround:

import SwiftUI

#if canImport(UIKit)
import UIKit
extension Color {
    init?(systemName: String) {
        let sel = Selector(systemName)
        guard UIColor.self.responds(to: sel), 
            let result = UIColor.self.perform(sel) else {
            print("no such system, color: \(systemName)")
            return nil
        }
        let object = result as Unmanaged<AnyObject>
        let color = object.takeUnretainedValue() as! UIColor
        self.init(color)
    }
}
#endif

#if canImport(Cocoa)
import Cocoa
extension Color {
    init?(systemName: String) {
        let sel = Selector(systemName)
        guard NSColor.self.responds(to: sel), 
            let result = NSColor.self.perform(sel) else {
            print("no such system, color: \(systemName)")
            return nil
        }
        let object = result as Unmanaged<AnyObject>
        let color = object.takeUnretainedValue() as! NSColor
        self.init(color)
    }
}
#endif

Should work for both UIKit and Cocoa clients utilising Obj-c's performSelector feature. Minimally tested.

PS. forgot to mention: systemName should be in the form: "systemRedColor", "systemBlueColor" and so on.