Background color cannot be changed

## Description
The background color cannot be changed

## Steps to reproduce

1. Go to http://leonardocolor.io
2. Click on Create new theme
3. Observe the default Color scale "Gray"
4. Observe the tab "Theme colors" is selected
5. Observe the palette generated from the color scale Gray
6. Observe the Background color cannot be changed
7. Click on the "Theme Settings icon"
8. Click on "Background color"
9. Observe only "Gray" is available to select
10. If you add more colors to the Color scale, selecting those colors as the Background color does not change anything.

## Expected behavior
The Background color should have the option to input a custom color value.
Nothing happens when you click on it except copying the current value (#FFFFFF) to clipboard.

## Screenshots

## Environment
MacBook Pro M1 (16-inch, 2021)
MacOS 12.4
Version 100.0.4896.127 (Official Build) (arm64)

## Additional context
N/A

Reproduce the issue at leonardocolor.io by creating a new theme and opening Theme Settings > Background color. Start by tracing the Theme Settings background-color control and how its selected value is applied to the generated palette. Done means a custom color can be entered or selected, and changing it updates the background color rather than only copying #FFFFFF.

Written by the indexing model from the issue text.