Exporting as PNG does not give the background/color for the annotation

**Describe the bug**
When exporting a brush annotation as a PNG, the output is not mapped by the background colors specified in (Settings > Labeling Interface). In addition, when exporting as a JSON, the background colors for the attributes are not specified anywhere, leaving the values that were selected in the interface as arbitrary and as not linked to any of the outputs.

**To Reproduce**
Steps to reproduce the behavior:
1. Go to Projects page for a certain project (should see Projects/ in the top left corner)
2. Click on Export on the top right banner above the image list
3. Select 'Brush labels to PNG' or 'JSON'
4. In the case of the brush label output, there isn't a consolidated image with color
5. If I was to use the JSON to convert to an image format, the background color of each label isn't provided in the export either.

A different, but related issue, to our use of the product is if there's a functionality to prevent overlapping of labels (only 1 label at maximum is applied to each pixel)? If so, how can we configure it?

**Expected behavior**
Ideally, I would be able to export an image that by design associates each color to their respective label region.

**Environment (please complete the following information):**
- OS: Linux CentOS
- Label Studio Version 1.4.1