I just created a portal on a layout (with a background photo) that is used on iOS with FM go app as well as the web with Safari/Chrome. The portal is visible only when it has records to show and it should be transparent (only show the text in the records). This works fine with the "hide" calculation and "no background" (full transparency) on MacOS Sierra FM client and iOS 10.2 via WebDirect FM go client. But not on the normal web with Safari or Chrome. Instead the portal is always there on the web, empty with a solid white background. Why? The only explanation I can see is that portals don't support transparency on all platforms. Or...?
I temporarily added "don't show portal at all" on the web [Get(systemplatform)=4] but it's not a great solution.