Navigation bar background color changing

**Describe the bug**
I updated from version 5.6.1 to 5.7.2 and I now have a scrolling nav bar that change color after scrolling or navigating to another controller. Note that my nav bar has it's color set using appearance at the beginning of the app, but somehow it changes from white to grey.
This bug was probably introduced by #392 or #399.

**To Reproduce**
Steps to reproduce the behavior:
1. Set the background/tint color of all UINavigationBar to a light color using appearance when the app starts
2. Make a controller with a scrollview that has a dark background color and a scrolling nav bar on top
3. Start the app and scroll to reduce the nav bar and scroll to top again or push an other view controller and come back

**Expected behavior**
The color of the scrolling nav bar should stay the same

Start by reproducing the behavior in AMScrollingNavbar on version 5.7.2 using a UINavigationBar configured through appearance, a dark scroll view, and the scrolling navigation bar. Exercise the bar by scrolling down and back up, then by navigating away and returning. Done means the navigation bar retains its configured light background color in both cases.

Written by the indexing model from the issue text.