I'm in the process of bringing one of my apps back from Kodular to AI2 or importing it into Niotron. That's already complicated enough. But now I notice that it is not possible to display buttons with transparent color in AI2. With Kodular it works as expected. I actually can't believe I only noticed this today. (The same with Niotron, by the way.)
Did I miss anything here?
Try with 16777215 as the colour number ?
Well it is transparent, just that the device default theme gives it a shadowed border (changing from default to rectangular, etc., makes no difference (works OK in Classic). There may be an extension that can clear this border...
No, not there either.
The only option for now is to use appropriate transparent images (png).
Thanks to the collaboration between Kodular and AI2, everything should work in the end.
"Wer's glaubt, wird seelig" oder "Die Hoffnung stirbt zuletzt", wie man in Deutschland sagt. 
"Anyone who believes it will be blessed" or “Hope dies last,” as they say in Germany.
Does with companion...
I don't want a complete transparent button but something like this:
This works, but strangely, setting the background color to "none" in the designer does not seem to do anything (using the companion).
Perhaps this a known bug I'm unaware of.
The background color of the button itself is transparent. It's just the shadow that's present on every button. There might be an option to remove the shadow to make the button "totally" transparent.
So I took a bit of time to look into this and it does appear like the blending is also taking into account the default button color provided by Android, which leads to the off coloring. I've worked on a potential fix and we will see about getting it into the upcoming release.
I was unable to reproduce this look of Button2 and 3 - on any of my test devices running Android 5-13). In each case, the colors were NOT transparent, regardless of the level of transparency.
Screenshot from Pixel 4XL, Android 13:
Right. The pull request I linked will fix the problem. My screenshot was taken with a version of App Inventor with that change applied. In the coming days we'll be updating the test server with a draft of the next version, so once that's available you should be able to try it out.
