Color Transparent

I have been working on a project involving editing photos using VB for a while. I used to use a picture box as a transparent overlay by changing its back color to transparent. That behavior changed a couple of years ago. I assumed they changed picturebox's behavior.

I, recently, tried making a clear hole thru an image by FillEllipse method with color.fromargb(0,0,0,0). That didn't do anything either. Only way I found was by changing pixels one by one. That resulted in a noticeable delay in an interactive process. Painting with color.transparent should change the pixels to transparent like all the other colors do.

If you cannot get a gloss or satin version what would you use a clear coat for?