WebEngineView "backgroundColor" has no documentation

https://doc.qt.io/qt-5/qml-qtwebengine-webengineview.html#backgroundColor-prop

I want to set this as P2 as the feature is slightly useless in its current state of being undocumented. Putting "bool" next to it doesn't exactly help. There's no documentation here or on third party resources as to what colors will fit in there, QColor's defined formats do not work either. Nothing works like it should as noted by the resources, or at least... nothing I've tried yet. It's hard to tell when I throw literally anything into those quotations and hope that something will happen.

e.g. "transparent" works (that's good...), "#FF000080" works to get a slightly transparent blue, "#FFFF0080" works to get a slightly transparent red. But the moment I try to use it like an actual RRGGBBAA hexadecimal item, nothing works anymore and the whole thing goes transparent. https://kilianvalkhof.com/2016/css-html/css-hexadecimal-colors-with-transparency-a-conversion-tool/ things that this tool gives me will not work, it will result in an entirely transparent background as if it just broke. e.g. this will not work

backgroundColor: "#1C1C1CCC"

Whereas this will work

backgroundColor: "#FFFF00CC"

Is it not following standard conventions? If not, then what convention does it follow? This needs to be documented.

Qt version: 5.12.3

These are the imports for that file:

import QtQuick 2.7
import QtWebEngine 1.5
import QtWebChannel 1.0