Access Environment variable in extensions

In a View I can access the environment variables with the @Environment property wrapper like this:

struct MyView: View {

    @Environment(\.colorScheme) var colorScheme: Color

    var body: some View {
        Text("Hello")
            .foregroundColor(self.colorScheme == .light ? .black : .white)
    }
}

In an extension, this is not possible, because I cannot put variables to an extension. How can I access the @Environment values in an extension, for example if I want to extend Color?

Until now I found out, that I can use Environment with the wrappedValue property like this:

extension Color {
    static var darkModeText: Color {
        if Environment(\.colorScheme).wrappedValue == .light {
            return .black
        } else {
            return .white
        }
    }
}

The problem is, that this doesn't gets updated and always contains .light. I also tried using @Environment as a global variable, but this is (not yet) supported by property wrappers.