[ux] Layer items don't match their expected colors in the Usability Hub Topping Maker Wizard for non-default QGIS themes

[gacarrillor]

This is how LayerModel items look like in non-default QGIS themes:

The issue

The LayerModel.data()'s returned value for the Qt.BackgroundRole role is being overridden by a global stylesheet set by the non-default QGIS themes (like Night Mapping theme):

QTreeView::item, QTreeView::branch {
	background: transparent;
	color: @textlight;
}

One might expect that even having a global stylesheet, one could set the item background via Qt.BackgroundRole, but the current behavior is well known in Qt and considered as a feature, rather than a bug. For reference, some related links:

https://forum.qt.io/topic/95940/model-backgroundrole-overridden-by-style-sheet
https://bugreports.qt.io/browse/QTBUG-70100

Suggestion

Instead of using colors, add a text clue for non-INTERLIS layers (e.g., My Layer*) and in the legend below the QTreeView, replace color symbols by something like *: Non-INTERLIS layer.