Color enum values are not recognized as color by the Variable Completer popup

1 - Create new document in the builder
2 - Add a stylesheet containing
:root {
--my-own-color: blue;
}

.my-style {
height: 100px;
}
3 - Select .my-style selector
4 - In the Inspector, right-click on the label of the Background/Color field and select "Set to Variable"
5- Type "--my-own-color" in the Variable Search field

Expected:
When typing "--", the auto-complete list will display the --my-own-color variable

Actual:
The auto-complete list does not contain the --my-own-color variable

Jira Issue: https://jira.unity3d.com/browse/UIT-1311