UIViews losing their backgroundColor during transition

## What did you do?

In my project, there are a series of UIViewControllers that all share a common background UIImageView. Using Hero, I set `navigationController?.hero.isEnabled = true`. Then I set the `heroId` of the imageView that contains the same image from each ViewController.

```
self.bgImageView.hero.id = "bgImageView"
nextVc.bgImageView.hero.id = "bgImageView"
```

I then call `pushViewController`

## What did you expect to happen?

I would expect the background image to persist during the transition, but for the other elements to be replaced in the slide animation.

## What happened instead?

This does happen, however UIViews that have their backgroundColor set lose their backgroundColor and become clear during the transition.


If I remove the hero identifiers on the background imageView, the UIButton and UITextField's act as expected, retaining their backgroundColor.

## General Information

* Hero Version: 1.5.0

* iOS Version(s): 13.4

* Swift Version: 5

* Devices/Simulators: iPhone 11 Pro Simulator, iPhone 11 Pro

* Reproducible in Examples? (Yes/No): Yes

## Demo Project

https://github.com/logananderson/HeroIssueExample