Lighten or darken identicon

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

@@ -118,6 +118,7 @@ public class AdapterMessage extends PagedListAdapter<TupleMessageEx, AdapterMess
     private boolean debug;
 
     private int dp24;
+    private String theme;
 
     private SelectionTracker<Long> selectionTracker = null;
 
@@ -292,7 +293,9 @@ public class AdapterMessage extends PagedListAdapter<TupleMessageEx, AdapterMess
             }
             if (!photo && identicons) {
                 if (message.from.length > 0)
-                    ivAvatar.setImageBitmap(Identicon.generate(((InternetAddress) message.from[0]).getAddress(), dp24, 5));
+                    ivAvatar.setImageBitmap(
+                            Identicon.generate(((InternetAddress) message.from[0]).getAddress(),
+                                    dp24, 5, "light".equals(theme)));
                 else
                     ivAvatar.setImageDrawable(null);
                 photo = true;
@@ -1409,6 +1412,7 @@ public class AdapterMessage extends PagedListAdapter<TupleMessageEx, AdapterMess
         this.debug = prefs.getBoolean("debug", false);
 
         this.dp24 = Math.round(24 * Resources.getSystem().getDisplayMetrics().density);
+        this.theme = prefs.getString("theme", "light");
     }
 
     private static final DiffUtil.ItemCallback<TupleMessageEx> DIFF_CALLBACK =

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

@@ -9,8 +9,10 @@ import android.graphics.RectF;
 import java.security.MessageDigest;
 import java.security.NoSuchAlgorithmException;
 
+import androidx.core.graphics.ColorUtils;
+
 class Identicon {
-    static Bitmap generate(String email, int size, int pixels) {
+    static Bitmap generate(String email, int size, int pixels, boolean dark) {
         byte[] hash;
         try {
             hash = MessageDigest.getInstance("MD5").digest(email.getBytes());
@@ -18,12 +20,15 @@ class Identicon {
             hash = email.getBytes();
         }
 
+        int color = Color.argb(255, hash[0], hash[1], hash[2]);
+        color = ColorUtils.blendARGB(color, dark ? Color.BLACK : Color.WHITE, 0.2f);
+
         Paint paint = new Paint();
-        paint.setColor(Color.argb(255, hash[0], hash[1], hash[2]));
+        paint.setColor(color);
 
         Bitmap bitmap = Bitmap.createBitmap(size, size, Bitmap.Config.ARGB_8888);
         Canvas canvas = new Canvas(bitmap);
-        canvas.drawColor(Color.argb(255, 128, 128, 128));
+        canvas.drawColor(Color.TRANSPARENT);
 
         float psize = (float) size / pixels;