During WWI the German Fliegertruppe use the Phosphor bullets to observe the Fireline from the MG`s.
In WWII the MG 15, 17, 81Z used the 7,9mm Patrone S.m.K.L'spur 100/600. The tracer start to burn from 100 meter until 600 meter. The colour where in green or yellow.
For nightuse there was the same bullet with a less visible "Glimmspur"