The tutorial at this location: https://defold.com/tutorials/grading/ is out of date.
It mentions usage of “render.enable_render_target” and “render.disable_render_target” however these no longer exist. However, I do see https://defold.com/ref/render/#render.set_render_target:render_target-[options] as an option. I tried following the tutorial up to the point of creating a grayscale filter effect however I only see a black screen (with my HUD elements drawing over it.) I am using set_render_target and render.set_render_target(render.RENDER_TARGET_DEFAULT) to return to the framebuffer instead of the enable/disable functions mentioned.