I looked into this before and I have a feeling it should be possible, but I wasn't able to figure it out. I think the difficulty I was running into last time was retrieving the Websocket ID or something like that. I believe the message handler system uses the Websockets protocol so, from my understanding, you could theoretically send a message from the UI to a backend script (?). That would be such a clean solution - send a message from iframe and receive on the Perspective view - that would greatly minimize the need for creating custom modules to wrap certain javascript components, for example.
I think it's impossible natively in html with a color input.
The easiest way seems to be to use a slider on the side to manage the opacity.
Hi did you have last version on this feature, I have a project in which I have to drag this horizontally.
