Well thickness doesnt have a bearing on the darkness , and No3 is dark enough so as not to see in ,the real helmet is No3 in darkness,
Also in ESB the visor looks grey any way (I think it was smockeds tint like the other helmets in the filming of ESB ), its green in the ROTJ S.E
but you should try a Jacksons protective face shield ,welding visor or n green safety visor