I just open the lower parts kit I got from Model1 and noticed that some of the components are different colors; is this normal?  My mag release, front takedown pin, and safety selector are green while all my other parts are various shaded of dark grey / black.  Where can I go to get black replacements for the green parts?

Don't know if you'd call it "normal", but it is fairly usual. Part of it is the difference in materials. Things like the aluminum trigger guards and mag release buttons are aluminum, and most aftermarket suppliers will give you pieces that have been black anodised, rather than the charcoal finish of the lower reciever.

The steel pieces, selector levers, takedown push pins, triggers, mag release and bolt holdopens, are invariably subcontracted parts, phosphate finished, and usually acquired from different subbies. Their color will depend on 1)the type of steel that was used, 2)the type of phosphate finish applied, and 3)the length of time the piece was left in the bath tank.

The only way you can be assured of getting a fairly close color match, I believe, is to find a parts dealer at a gun show who will let you paw thru his stock of the various pieces to color match your parts[:D]