Revert "Always set card background color"

This reverts commit 9ca9a86416.

app/src/main/java/eu/faircode/email/ViewCardOptional.java

@@ -37,6 +37,7 @@ public class ViewCardOptional extends CardView {
     private boolean threading;
     private int margin;
     private int ident;
+    private Integer color = null;
 
     public ViewCardOptional(@NonNull Context context) {
         super(context);
@@ -82,12 +83,16 @@ public class ViewCardOptional extends CardView {
 
     @Override
     public void setCardBackgroundColor(int color) {
-        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getContext());
-        boolean cards = prefs.getBoolean("cards", true);
-        if (cards && color == Color.TRANSPARENT)
-            color = Helper.resolveColor(getContext(), R.attr.colorCardBackground);
+        if (this.color == null || this.color != color) {
+            this.color = color;
 
-        super.setCardBackgroundColor(color);
+            SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(getContext());
+            boolean cards = prefs.getBoolean("cards", true);
+            if (cards && color == Color.TRANSPARENT)
+                color = Helper.resolveColor(getContext(), R.attr.colorCardBackground);
+
+            super.setCardBackgroundColor(color);
+        }
     }
 
     public void setOutgoing(boolean outgoing) {