refactor: update default colors in PanelColorSettings

[JoshuaHungDinh]

Resolves: https://stellarwp.atlassian.net/browse/GIVE-807

Description

This PR includes a temporary fix for the PanelColorSettings default color list. The original default colors included "White" which could not be seen on the form. It along with the rest of the default colors to choose from have been updated. In the future we will look into integrating theme.json for the Visual Form Builder to handle presets.

Affects

Visual Form Builder

Visuals

Testing Instructions

• In the Visual Form Builder, open the Styles sidebar in Design mode
• Select both color controls and verify the new default color list.

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Reviewed by the designer (if follows a design)
• Self Review of code and UX completed

[pauloiankoski]

👏🏻

[rickalday]

Passed manual QA tests.