Injector o-ring differences

[Musicars]

I have the intake off the engine I am getting ready to put in my Denali. I figured I would take the injectors out, clean them, and put new o-rings on them. I got an ACDelco kit that came with all blue o-rings and the part number is listed as correct although it as since been superseded by a newer one. The injectors currently have blue on top and brown on the bottom. I can't find concrete information on whether or not the colors represent different materials or not. I assumed blue ones were neoprene and brown ones were Viton but not sure if that is true or even makes any difference. One source listed the brown ones as for flex fuel engines. Any thoughts?