As pointed out by Christian, the visual spec seems to require the context menu to be a Dialog (which would give the greyed out background for free). However, the modal nature of the dialog seems to clash with the contextual nature of the menu: if a user invoked the menu by accident, she should be able to dismiss it by tapping outside of it, which the dialog component doesn’t seem to permit.
As pointed out by Christian, the visual spec seems to require the context menu to be a Dialog (which would give the greyed out background for free). However, the modal nature of the dialog seems to clash with the contextual nature of the menu: if a user invoked the menu by accident, she should be able to dismiss it by tapping outside of it, which the dialog component doesn’t seem to permit.