The original trigger group parts which had the tendancy to wear to a point to cause unexpected and uncontrollable doubles, triples, and full auto, were the same black phosphate color as the rest of the gun. When Glock redesigned the contours and dimensions to prevent this, they also changed the finish to a hard chrome, because there had been a seperate issue with corrosion on the small parts. (Small parts are not given the tenifer treatment.). Thus, all the "upgraded" trigger parts were/are chrome. Therefore when we speak of original trigger group parts, they can/are referred to as "black parts".