Fix broken ColorDisplayServiceTest cases

Bug: 133173665
Test: atest FrameworksServicesTests:ColorDisplayServiceTest
Change-Id: Idb1ca2122bf5f5453fa4a890afc6a810e46cf532
diff --git a/services/core/java/com/android/server/display/color/ColorDisplayService.java b/services/core/java/com/android/server/display/color/ColorDisplayService.java
index 27acb6b..2e5aafe 100644
--- a/services/core/java/com/android/server/display/color/ColorDisplayService.java
+++ b/services/core/java/com/android/server/display/color/ColorDisplayService.java
@@ -226,7 +226,7 @@
         }
     }
 
-    private void onUserChanged(int userHandle) {
+    @VisibleForTesting void onUserChanged(int userHandle) {
         final ContentResolver cr = getContext().getContentResolver();
 
         if (mCurrentUser != UserHandle.USER_NULL) {