Hi Tgoy, for the edit frame corners that appear around the selected objects, that can be modified in moi.ini under:

[View]
<...>
EditFrameOpacity=45

That can take a value between 0 (fully transparent) to 255 (fully opaque). You can edit the moi.ini file by going to Options dialog > General > "Edit .ini file" button.


In the v5 beta the view controls that are at the bottom of viewports has opacity controlled by the current UI theme. You can create a new theme and modify the value under Options > General > Manage themes > Viewport > "View controls opacity". That also takes a value from 0 to 255.

- Michael