How did the green-grey parts (where the blue health bar and rocket propelled grendades happen) become slightly translucent in game?
The GUIOverlay.tif file itself when opened in Photoshop has no transparency and those areas are a solid green-grey. Is it a function of the colour it’s set to in the Inspector?
You almost gave the answer yourself. The color set for the GUIOverlay GUI texture has its “opacity” component set to about 50%
I don’t have photoshop, but I can see that when I look at the texture, and choose “show alpha” that there is an alpha channel, but you are correct that it is completely opaque for the “border” parts.
I believe that the opacity of “Color” in the material setting and the alpha from the texture are multiplied to give the alpha actually used for blending. Just like the R, G, and B components of the color.