Dear @DCzarnowski, many thanks for flagging, apologies for the late response.
As it happens opacity is off the list of attributes queued up for dynamic updates in PsychoJS at the moment, but you’ll be pleased to know a patch is on the way.
For your convenience, I have prepared a fork that includes a local PsychoJS lib folder containing the fix, if you are happy copying those files over to your project.
The only thing is, when you export HTML again as you further develop your experiment, you will then have to each time manually edit line #9 to import from ./lib/visual-2020.2-patch.js.
That is no doubt annoying, which is why I will for sure be following up here in the coming days to let you know that a permanent fix has been made available on Pavlovia.
Please let me know if you need more support, here to help, s.