Xfce inactive desktop icons have solid light gray background.

[regs01]

That's because in the beginning there is explicit .view:backdrops

skeuos-gtk/src/sass/gtk3/upstream/_common.scss

Line 113 in 095e06a

&:backdrop {

Which is not being cancelled for XfdesktopIconView.view

skeuos-gtk/src/sass/gtk3/_applications.scss

Line 192 in 095e06a

XfdesktopIconView.view {

Adding XfdesktopIconView.view:backdrops would fix it.

XfdesktopIconView.view,
XfdesktopIconView.view:backdrops {
  background-color: transparent;
  color: white;
  text-shadow: 0 1px 2px black;
}