Replace lock PNGs with a vector drawable.

app/src/main/java/org/fdroid/fdroid/views/AppDetailsRecyclerViewAdapter.java

@@ -975,7 +975,7 @@ public class AppDetailsRecyclerViewAdapter
 
         @DrawableRes
         protected int getIcon() {
-            return R.drawable.ic_lock_24dp_grey600;
+            return R.drawable.ic_lock;
         }
     }
 

app/src/main/res/drawable/ic_lock.xml

@@ -0,0 +1,5 @@
+<vector android:height="24dp" android:tint="#B4B4B4"
+    android:viewportHeight="24" android:viewportWidth="24"
+    android:width="24dp" xmlns:android="http://schemas.android.com/apk/res/android">
+    <path android:fillColor="#FFFFFF" android:pathData="M18,8h-1L17,6c0,-2.76 -2.24,-5 -5,-5S7,3.24 7,6v2L6,8c-1.1,0 -2,0.9 -2,2v10c0,1.1 0.9,2 2,2h12c1.1,0 2,-0.9 2,-2L20,10c0,-1.1 -0.9,-2 -2,-2zM12,17c-1.1,0 -2,-0.9 -2,-2s0.9,-2 2,-2 2,0.9 2,2 -0.9,2 -2,2zM15.1,8L8.9,8L8.9,6c0,-1.71 1.39,-3.1 3.1,-3.1 1.71,0 3.1,1.39 3.1,3.1v2z"/>
+</vector>