When I am searching the colour of Mg3N2 I came across photoes showing Greenish Yellow(https://upload.wikimedia.org/wikipedia/commons/7/7b/Magnesium_nitride.jpg)

 and some other Just yellow(https://www.google.com/search?q=magnesium+nitride&client=ms-android-samsung-gj-rev1&prmd=ivn&sxsrf=ACYBGNSoIGFwKl13pCTUnuLG56Z3AXGi8A:1577325847492&source=lnms&tbm=isch&sa=X&ved=2ahUKEwjCydbWnNLmAhXm4zgGHZ-MDwoQ_AUoAXoECBAQAQ&biw=360&bih=660&dpr=2#imgrc=vQsxB_VNrj3WfM), I am eager to know what causes some samples to be bit greenish