ui: avoid alpha 0 on images with Mask dependency across PledgerSkin

src/Decentralized/WalletWindow.cs

@@ -195,7 +195,7 @@ namespace Decentralized
                 OnClick = () => { dev.Asset = x.asset; dev.Note = null; Open(dev); }
             });
             PledgerSkin.Apply(win, screen, bezel, paper, _picked, _clear, rows);
-            if (plate != null) plate.color = PledgerSkin.Transparent;
+            if (plate != null) PledgerSkin.SetClear(plate);
             // 签名要按住 ✓：在按键上挂一个按住计时
             if (ok != null && dev.Screen == Screen.Review && ok.GetComponent<HoldToSign>() == null) ok.AddComponent<HoldToSign>().Device = dev.Address;
         }