Used a constant instead of magic number for colour

Explicitly stated the blending mode

OpenKeychain/src/main/java/org/sufficientlysecure/keychain/ui/ViewKeyActivity.java

@@ -33,6 +33,7 @@ import android.content.Intent;
 import android.database.Cursor;
 import android.graphics.Bitmap;
 import android.graphics.Color;
+import android.graphics.PorterDuff;
 import android.net.Uri;
 import android.nfc.NfcAdapter;
 import android.os.AsyncTask;
@@ -924,7 +925,7 @@ public class ViewKeyActivity extends BaseSecurityTokenNfcActivity implements
                                     }
 
                                     mPhoto.setImageBitmap(photo);
-                                    mPhoto.setColorFilter(Color.argb(30, 120, 166, 69));
+                                    mPhoto.setColorFilter(getResources().getColor(R.color.toolbar_photo_tint), PorterDuff.Mode.SRC_ATOP);
                                     mPhotoLayout.setVisibility(View.VISIBLE);
                                 }
                             };