Steps to reproduce:

1. Open a Unity project
2. Open the UI Builder via Window > UI Toolkit > UI Builder
3. Create a Visual Element by dragging it from the Library to the Hierarchy
4. Make sure the Visual Element is selected and that its details are visible in the Inspector
5. Find the color option under Inlined Styles > Background
6. Using the color picker window, select a background colour for the element

Actual results: The Visual Elements colour does not change in the canvas. The reason for this is that by default, the Alpha value of colours are set to 0 in UI Builder

Expected results: The Visual Elements colour changes to the colour set in the color picker window

Reproducible with versions:

• 6000.0.13f1
• 2022.3.39f1

Not reproducible with versions: 

• 2021.3.40f1 (different functionality, see notes)

Can’t test with versions: - 

Tested on (OS): Windows 10, Windows 11

Notes:

• Multiple internal users across QA have used UI Builder in the past and have ran into the issue of not knowing that Alpha is by default set to 0. It personally took me a while of thinking that the functionality was broken, and needing to ask around, before realizing that my issue was that Alpha was set to 0 and needed to be changed.
• In 2021.3, this is not a usability issue. In this version, Alpha is set to 1 by default and so changing the colour will affect the background colour without needing to set the Alpha. The reason why in this version there isn't a background by default is that UI Builder does not set the USS until the property is edited (so there is no background colour defined in the style). This is much more intuitive and doesn't have some users thinking the functionality isn't working if they don't notice that Alpha is set by default to 0.