The order of which function argument expressions are executed is
undefined, so don't rely on this for setting the background colors, as
it results in different colors on different architectures.
For example, it has been observed that the order of execution is
reversed comparing x86_64 and aarch64, making these two architectures
having different background color.
Fix this confusion, and also reproduceability in future reference tests,
by making the order of execution predictable.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1698>
ba38057067