Label image volume is not visible outside of intensity image bounds in `view`

## Overview

When viewing two binary images with `view(image1, label_image=image2)`, only the first image volume is displayed. The second image volume can be inferred as intersections on the label surface.


## Expected Behavior

Two volumes of different colors are visible in the scene.

## Observed Behavior

One volume is visible as a 3D boundary. The intersection of the other volume is implied as discoloration on the first volume surface.

## Minimum Reproducible Example

```py
arr1 = np.zeros([25,25,25], dtype=np.uint8)
arr1[1:15,1:15,1:15] = 1
image1 = itk.image_view_from_array(arr1)

arr2 = np.zeros([25,25,25], dtype=np.uint8)
arr2[:20,:5,:5] = 1
image2 = itk.image_view_from_array(arr2)

itkwidgets.view(image1, label_image=image2)
```

Intersection in red:


cc @PaulHax