Sublayers opaque to each other but semi-transparent as a unit

[ebbishop]

I've built a custom MVTLayer that renders a set of sublayers (GeoJSONLayers and a TextLayer). I'd like them to be opaque to each other but semi-transparent as a unit. Is this possible with the basic layer config options? I've set the getLineColor and getFillColor of each sublayer to use opaque colors, and explicitly set the opacity: 1 for each sublayer. This does make the sublayers opaque to each other, but setting opacity: 0.6 on the parent layer doesn't seem to have an effect. Is this expected? If so, is it possible to override this behavior?