I just fixed this for the next release v18.09. Will have to wait a while unfortunately. In the meantime, you can filter a transparent color clip and export using the Quicktime Animation export preset mentioned in the linked topic. Or, you can open a clip in Source player, trim and filter it, and export it (pay attention to the From field at the top of the Export panel) as some intermediate or lossless format. Then, use either of those in a larger project.