Which part in the editor's source code setting the axis of edit tool transparent?

Hi guys!
I want to draw a edit tool in the runtime game, I just used some codes of the editor source code.And a lot of difficulties I have met…Now I already can draw a coordinate axis with “UPrimitiveComponent”, but my axis can’t be transparent,it will be hidden by other meshes.I know it has a relevant with material,but I just can’t find which part of the editor source doing this things.
here is what the problem look like:

83444-qq截图20160323141802.png

Another question by the way: how can I use the Hhitproxy without modify the engine code,or just do the same effect (detect which axis the cursor is on) by some other way.
thanks a lot .