I am wondering how can I change the glass color (transparency) in GTK3? For example, if one hits the hot-spot corner (top-left) and you go to the applications display, there is a layer of glassy sheet. How can I make that brighter because, now, I have black icons?
I think this cannot be changed easily, Since this is the default gtk3 theme for gnome-shell (name is Adwaita). But you can use other gnome-shell themes.
Here is the description of the theme quoted:
Then use gnome-tweak-tool to enable User theme extension. Then quit. Again start gnome-tweak-tool and select the theme you want from Shell Themes menu.
Hope this will helps.