immediate OGL calls?
More like single vertex calls like glColor(1,1,0,1) etc.
I am not seeing any issues right now with my approach either, I am not really looking for alternatives right now
There's nothing wrong with your approach.
but its kind of something you don't see talked about too much, I've seen all kinds of shaders for example, but not one specific to GUI rendering, so I was just wondering if there was some sort of defacto way to do it I didn't knew about.
In fact you can render your whole gui as 3d mesh (consisting of multilayered quads in front of a orthogonal camera). This way you could utilize some interesting effects, e.g. dynamic lighting of the gui, where the cursor is the light source, or automatic highlighting/bloom outlines of selected elements, gui shadows etc. This is not for pure functional guis, but it is really nice to pimp your gui visuals :)