tweak system message background colors

deltachat-ios/Controller/ChatViewController.swift

@@ -737,7 +737,7 @@ extension ChatViewController: MessagesDisplayDelegate {
         if isInfoMessage(at: indexPath) {
             return .custom { view in
                 view.style = .none
-                view.backgroundColor = UIColor(alpha: 10, red: 0, green: 0, blue: 0)
+                view.backgroundColor = DcColors.systemMessageBackgroundColor
                 let radius: CGFloat = 16
                 let path = UIBezierPath(roundedRect: view.bounds,
                                         byRoundingCorners: UIRectCorner.allCorners,

deltachat-ios/Helper/Colors.swift

@@ -16,6 +16,7 @@ struct DcColors {
                                                      dark: UIColor(red: 10 / 255, green: 10 / 255, blue: 10 / 255, alpha: 1))
     static let placeholderColor = UIColor.themeColor(light: UIColor(red: 0.6, green: 0.6, blue: 0.6, alpha: 1),
                                                      dark: UIColor(red: 0.4, green: 0.4, blue: 0.4, alpha: 1))
+    static let systemMessageBackgroundColor = UIColor.themeColor(light: UIColor.rgb(red: 248, green: 248, blue: 248), dark: UIColor(white: 0.2, alpha: 0.5))
 }
 
 enum SystemColor {