struct ContentView: View {
    init() {
        UITextView.appearance().backgroundColor = .clear // First, remove the UITextView's backgroundColor.
    }
    @State private var input = ""
    var body: some View {
        ZStack {
            Color.blue.edgesIgnoringSafeArea(.all)
            TextEditor(text: $input)
                .font(.body)
                .foregroundColor(.white) // Text color
                .background(Color.blue) // TextEditor's Background Color
        }
    }
}

从iOS 16开始，您可以使用

TextEditor(text: $notes)
    .scrollContentBackground(.hidden)