Rod Serling's narration says at the end of that the title phrase Purple Testament comes from the William Shakespeare play "Richard III". It is actually Richard II, Act 3, Scene 3.
Captain Riker and Lieutenant Fitzgerald are wearing their insignia. Officers serving on the Pacific Front made a point not to wear this because it identified them as high priority targets for Japanese snipers.
When the platoon confronts Lieutenant Fitzgerald about his ability to "see" death in soldier's faces, there is an African-American soldier in the back row. The US Army did not have integrated combat units until after WWII ended.
When Fitzgerald knocks his shaving mirror to the ground, it breaks (and is obviously glass). World War Ii military shaving mirrors were stainless steel.
The Philippine alcoholic drink is pronounced "tu-BA" rather than "toobah".